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General

Ground is responsible for all movements of aircraft on ground, except the movements on the runway. Ground takes over responsibility for Delivery if he is not online.

Your responsibility is strict: if you allow a plane to do something, the pilot can do without looking either way - you have to be sure the way is clear. This is, because big aircraft neither have a 360° view nor rear mirrors like a car has.

Phraseology

Start-up clearance

Start-up clearance can be given if no other aircraft is taxiing behind the starting-up aircraft and if the take-off is expected in 20 minutes or less.

Austrian 125, start-up approved, (Temperature Minus 3)

Push-back clearance

Push-back clearance can be given if no other aircraft is passing behind and the parking position requires push-back.

Austrian 125, push-back approved

Push-back is an approval - pilots are free to do it whenever they are ready. This means: It could take a while. This means: In busy conditions, you won't want that, as there is an aircraft which can push out any time and you cannot allow any other aircraft taxi behind. Several options are available to solve this problem:

Austrian 125, immediate push-back approved.

(the pilot has to say "unable" if he still programs the FMC)

Austrian 125, startup approved, call for push with running engines

(the pilot is ready for push and won't stand around on the taxiway trying to light his engines)

Combination of both phrases

During low traffic you can use these two phrases together

Austrian 125, start(-up) and push(-back) approved

Taxi Instructions

Bear in mind: Taxi instructions are clearances, that means: The pilot must and will do it regardless of other things - mainly aircraft around. Don't clear anyone for taxiing around without knowing that the way is free. Aircraft won't stop at junctions and look left or right (in most cases, they can't as they won't see enough).

The sequence is: The pilot pushes back and starts the aircrafts engines. As soon as he is ready for taxi he will call you:

AUA125:AUA125, ready for taxi.

Depending on traffic you can give him the taxi instruction to his departure runway:

GND:AUA125, taxi to holding point Rwy 16 via taxiways Exit 4, L and F, QNH 1019.
AUA125:Taxiing to holding point runway 29 via L and F, AUA125.

So how do you maintain traffic flow at a busy airport, but still maintaining safety? There is some options:

First is to clear the aircraft just as far as the way is free: "taxi to exit 32". "Taxi on E until intersection B4", and the like. But this is time-consuming, you loose overview, you forget aircraft on the way (they wait around for nothing), and it is slow too.

Second, and more elegant is the hold short argument:

GND:AUA125, hold short of taxiway L.
AUA125:Holding short of L, AUA125.

This means: The aircraft is cleared all the way to the holding point, but has to "hold short" (=to stop) in mid way for a condition which you specify. After that (that's the elegant part), he continues as cleared without further instructions.

This could be only to "hold short" --> until you tell him "continue".
It could be "give way to crossing B737 from your left to your right" --> the pilot will stop, wait for a passing 737 and continue.
It could be "follow company B737 taxiing on L" --> the pilot will look out for a B737 of his own color and follow him.
It could be anything else, provided that the pilot is able to do it, like 1 minute or whatever.

The "Hold short" argument puts some burden on the pilot: He must judge if he can meet the condition. If you tell a B747 to follow a C172, he might likely say "unable", as he is simply unable to see the little fly under his nose. As a controller, it is no good idea to tell pilots something they can't do (i.e. look behind) - pilots might oversee it and - bang.

Bear in mind that it is controllers' job to decide on wingspan room. Aircraft will taxi, and if you don't look out, this happens. If in doubt (as on VATSIM, you only have a scope and no window), warn the pilot and ask if he is able to pass without hitting anything.

At VATSIM, you sometimes meet pilots who apparently don't have charts and/or loose orientation - especially when it is dark and the scenery is bad. If a pilot starts sight-seeing, you can tell him to stop ("hold position") and to "expect progressive taxi", and that means: you taxi him step by step, and he is instructed to stop at every step. This is a good means to guide a lost aircraft around.

When an aircraft is approaching its assigned holding-point (and clear of possible traffic-conflict) a hand-off to next higher position (i.e. TWR) shall be initiated as soon as the aircraft is conflict-free in your area of responsibility. This means, if no other aircraft can be in the way on his way to the runway. Example for LOWW: Suppose, rwy29 is for departure. GND will line up all aircraft on taxiway M facing East, and TWR will pick them from there. Hand them over to TWR as soon as they approach the queue.

GND:AUA125, contact now Salzburg Tower on frequency 118.10, bye bye!
AUA125:contacting Tower on frequency 118,10 bye!

Air-taxiing is the Movement of a helicopter / VTOL above the surface of an aerodrome, normally in ground effect and at a ground speed of normally less than 20 KT (37 km/h). Please Note: The actual height may vary, and some helicopters may require air-taxiing above 25 FT (8 m) AGL to reduce ground effect turbulence or provide clearance for cargo sling loads.

OEATD: request air taxi to Runway 29.
GND: OEATD, contact TWR for further instructions.
OEATD: Servus Wien Tower, request air taxi to Runway 29 via Exit 13 and M.
TWR: OEATD, air taxi to Runway 29 via Exit 13 and M. wind 280 deg 5 knots
OEATD: air taxi to Runway 29 via M.

Ground Traffic Management

Bear in mind, that it is GND's job that he can taxi freely. If an aircraft has clearance, it can roll without looking anywhere else than straight ahead. You must see if the way is clear. But on a busy evening, you will have 5-10 aircraft taxiing at the same time. How you do this that they don't bump into each other, is called Ground Traffic Management.

To organise the traffic on ground different techniques are available, some of them relying on the pilots seeing each other. Generally you should avoid clearing two aircraft onto crossing pathways, unless you are sure they will never meet each other. To achieve this you should instruct aircraft to hold short of taxiways in the way stated above.

There are a few tools which you can use:

Taxiway configurations

Only one aircraft can taxi on a taxiway, so you have to order the traffic flow. On larger airports, you set the rules where outbound and where inbound aircraft roll. For LOWW, there is a nice document by Patrick Hrusa (thanks!). For LOWI, there is a nice LOWI_Primer by Claus and Hermann.

Step-by-step clearance

A very secure, but time-consuming way to control. Clear the aircraft only as far as it is definitely clear:

GND: AUA251, taxi to intersection M via E.
GND: AUA251, taxi to Exit 9 via M.
GND: AUA251, taxi to gate D21 via Exit 9.

You need a lot of time and patience for this, and with more traffic, you will end up in an overload soon.

Conditional clearance

This provides much more flow, but you have to think in advance. See, which aircraft approach to where and give one of them a conditional clearance to stop some point and give way. Make sure that the condition is clear: a specific intersection, a precise plane from a precise direction, like this:

GND: AUA251, taxi to gate D21 via E, M and Exit 9, hold short M for company A320 turning on M from your right.

"Conditional clearance" means: AUA251 is free to taxi until its final clearance limit (D21), but stops inbetween until the condition is met, in this case: another Austrian A320 taxiing (presumably on D) and turning in before him. Then, he is free to continue without instruction. "Hold short" means: You are cleared to your destination, but you should stop inbetween.

Intermediate instructions

Sometimes, things go differently as expected: Aircraft stop to sort out checklists, or they speed up. You might need to re-clear or stop the plane, like:

GND: AUA251, hold position, say again: hold position
GND: AUA251, continue.
GND: AUA251, hold short intersection W for a B190 crossing from your right to your left.
GND: AUA251, gate change, taxi to gate F1 via M, Exit 12 and taxilane 34, hold short Exit 12 and give way to B737 crossing from left to right.

Progressive Taxi

Some pilots don't know how to taxi, and some don't know where to taxi, and they can drive you mad. To them, you can issue progressive taxi instructions:

GND: Leipzig Air 600, hold position, expect progressive taxi.
GND: Leipzig Air 600, turn next left hold next intersection.
GND: Leipzig Air 600, turn right, on third intersection left and hold.

Consider the following situation:

You are the Ground Controller at Vienna Airport. Runways active are 34 for landing and 29 for departure. DLH6KM has vacated rwy 34 and requests taxi to its parking position. LZB421 is ready for taxi at stand B84.

GND:DLH6KM taxi to stand C40 via taxiway D and L.
DLH6KM:Taxiing to stand C40 via D and L, DLH6KM.
LZB421:Wien ground LZB421 stand 7B84, ready for taxi.
GND:LZB421, taxi taxiway M, hold short of taxiway L.
LZB421:taxiing via W holding short of L.

The aircraft are now both approaching the intersection L/W.

GND:LZB421, give way to the DLH B737 crossing left to right on L, thereafter continue
taxi to holding point runway 29 via taxiways Exit 2, M and A1.
LZB421:Giving way to the 737 from left to right, then continuing taxi to holding point
runway 29 via Exit 2, M and A1.

Of course you have to make sure that this instruction is unambiguous, so there shouldn't be two DLH B737s in the area. Also in low visibility operations this procedure might not work very well, in this case you might have to give the aircraft the instruction to continue taxi when the other aircraft has passed. In some cases it is also useful to let one aircraft follow the other:

GND:LZB421, follow the Austrian DASH 8 crossing you right to left on M to holding point runway 29.
LZB421:following the DASH 8 crossing us right to left on M to holding point runway 29.

Intersection departure

Some flights do not need the whole length of their given departure runway so they might request takeoff from an intersection somewhere down the runway. This procedure is called a intersection takeoff. You should only grant this in coordination with Tower and if traffic situation permits. Also at some airports intersections are used to be more flexible in the departure sequence (see section Departure Seperation).

Special Situations (High Traffic, Slots, ...)

Slots

In case the above mentioned slot regulations are in force ground has the responsibility to set up a departure sequence in a way that the aircraft do not miss their slot.

Opposite runway operations

At some austrian airports it is very common to use opposite runway configurations (departure and arrival runway are opposite to each other). In these situations it can happen very fast that you have two aircraft facing each other nose to nose. Special attention should be paid to avoid this situation.

Mind the wingtip: Size matters to GND controllers

As GND controller, you have to watch out for the size of an aircraft. You have two indications for the aircraft size in Euroscope: The Letter "L/M/H/S" in the flight strip, and the precise aircraft type in the departure list or tag - an abbreviation which you might need to google, but you will learn over time.

Light aircraft (L) need to go to stands, not to docks (you won't want to dock a Cessna, will you?). But "light" is not "light" - on some GAC aprons the aircraft has to be really light, especially when it comes to grass surface. Watch out to the aircraft type.

(A Cessna 172 taxiing in front of an A330:) Tower, confirm I should taxi before the Speedbird A330?
(Tower, smiling:) Confirmed, she's not hungry.

Medium aircraft have a different trouble: Some of them (like the Beech 99, the Dash or the Avro RJ are medium, but they need stands. Others, not much bigger, like the Fokker 70 or 100, can dock at the gate, whereas others (like the A319), only a little bigger, usually dock. In doubt: ask the pilot. The medium category goes up to the most-frequent cruisers A320 and B737.

Heavy aircraft are (almost) everything above: A330, B757, B767 and B747, the MD11 and the new B787. They almost exclusively dock, but there is another risk: Not all docks are suitable for heavies - ground charts tell you more. Look here to Vienna to see where you can park which birds.

Superheavy aircraft is in fact only one: The A380. There are no suitable docks for A380's in Austria - they park on large stands. Take care with those albatrosses when issuing taxi instructions: Many taxiways (like L in Vienna) are simply not made for this wingspan. [This] could happen.

More Information

If you really want to study hard, then read the relevant sections for GND in the official radio telephony guide from Austrocontrol.

A really good index (and much more orderly is here at Eurocontrol.