When in the line up waiting to been individually, make sure your horse has not fallen asleep so get his attention when the one before you is finishing off.
When you present yourself, don't plonk yourself right in front of the judge, the judges eye needs to cast over the whole picture and she should not have to move out of your way. Stand sqaure and a little smile always helps.
Walk away and do somethng short and sweet, figure of 8 trot and canter, use the ring and don't cut/rush round the corners, a short gallop (well fast canter) down the long length but don't stick the brakes on right at the last minute, it needs to smooth and controlled and show that your horse will push on without pony club kicking it to death down the ring side.
If you horse goes better on one rein than the other make sure you finish on that rein, for example if you horse get the wrong leg for falls in/out etc or stiff etc get that over with first so your last impression...and gallop is on the better rein rather than the sticky one.
Remember to go back into a nice active walk calmly back towards the judge, again stand your square near her not on top of her (or he) and if you can a nice short rein back, walk back into original position and little salute and say thank you and return back to the line up.
When riding round as a group, get yourself into a nice space, making sure there is plenty space in front of you and the next horse because they may go at a slower pace, if you do need to pass, do small circle back in but look first and work out where you going to join back in, its rude to push back infront of people specially when your all cantering around.
If you have a number make sure you know it, some stewards call you in by number rather than nodding at you.
When waiting to be picked don't gaze at the judge constantly like your desperate, just keep on careful eye on the steward but look where you are going.
Good Luck