Priorities change constantly depending on the traffic situation. If there are plenty of aircraft already at the holding point, then I'll tend to try and keep the inbounds moving (since the departure will only be sitting in a queue anyway) plus inbounds have more of a problem if they stop since all the punters immediately try and stand up! If you have a tight CTOT then you'll have a higher priority than otherwise. If it's very busy and three inbounds have the same route I might hold the outbound until all three have passed, rather than "threading" the outbound through (reduced RT workload). You might have high priority at one taxiway junction and low at the next, or vice versa. If you haven't been told whether to give way, then you should revert to the rules of the air (in the UK) eg give way to traffic from the right, towed traffic has priority over ac under their own power etc.
The gound situation is very dynamic at any busy airport, and priorities will change accordingly. Why not organise a visit to the tower and sit in on a busy GMC session, and the controller can explain some of the factors that affect our decisions?
