Be AEBF accredited.  Carry accreditation card at all times.
Have pen and small notebook, Ball marker and Timer [that counts down and issues and audible alarm when time runs out].
Dress Code:  Black slacks / trousers / skirt, Black hose and Black Shoes.
Either long sleeve white shirt / blouse [with collar], or as directed / supplied.
Check with Head Adjudicator / Tournament Direction for the following:-
a]   Session times and ensure you arrive a minimum of 15 minutes earlier.
b]   Any tournament By-laws etc.
c]   Dress code requirements of participants.
Up-to-date with the Playing Rules and “Calling Procedures”.
Ensure all calls are made ‘loud [without shouting] and ‘clear’ i.e. 30 seconds, 2nd Visit, Total Snooker granted etc.
Remember that calls must be able to be heard by both players involved in the match and the second Umpire [if one is used].
No doubt should be in anyone’s mind of what your call was / is.
Be polite in handling any queries of a player, but do not let a player continually question you during a frame.   If you are doing your job, they shouldn’t have to. If they do not know the rules, that is not your problem.
Do not remain static around the table.  It is in your best interests and the players for you to be ‘on the move’ checking out scenarios [balls touching cushions etc.].
If you are ‘on the move’ you will find that:-
a]   Your concentration level remains higher.
b]   You will be better able to predict the players option of play
c]   You will be able to check areas that may be a problem when the next shot is played, without alerting the player.
Once a player ‘goes down’ to play a shot, remain stationary.
Position yourself opposite the Baulk Line when a shot is to be played from baulk either on the Break or after a foul shot.  You cannot just guess whether the Cue Ball is in Baulk or on the Baulk Line
Do not retain possession of ‘rests, spiders’ or the like, dispose of them as soon as possible.
Do not hesitate to make calls regarding Loss of Frame,  Coaching and Breach of Spirit if they occur.  It is what is required of you.
Enjoy the match and leave it, knowing you did a good job.