I'm a total equitation freak, and so is my trainer (that's where I get it from (: )
Here's what I do:
1. Lots of no stirrups! Sometimes just taking them off your saddle is great too. Warm up a lot without them, then eventually work your way up to jumping singles and courses without them.
2. Do lots of exercises. For example, dropping one stirrup and posting, practice your 2-point or jumping position at the walk trot and canter, stand up at the walk trot and canter, trot fences, drop changes and lead changes, sit trot, hand gallop, etc etc etc. The better you are on the flat, the better you are over fences!
3. Do a lot of jumping fences, going straight and stopping. This will help your horse learn to go straight, without hesitation for the turn. After you and your horse get this down, practice some easy roll backs, bending lines, trot fences out of a roll back, etc.
4. Gymnastics lines are amazing! I love them because I can practice doing no stirrups down lines, and it helps your horse's form over the fences, which is always a plus.
5. Keep your back straight, and practice good posture! A nice straight back with even shoulders (not rounded, thats probably the ugliest thing an equitation rider can do in my opinion) always looks great in the pen. Also, be aware of your elbows, hands, heels, and legs. Elbows should have a moderate bend in them (you don't want them to be straight.. also looks ugly IMO) and should not excessively move, legs should be as still as possible (no stirrups will help make this second nature to you, and you won't have to worry about it!), heels should be down, and I personally like a small arch in the back.
You also want to be as soft as a rider as possible. You don't want to over exaggerate the 2-point. For example, let the horse come to you, not the other way around. Don't force it to happen, and don't get in too much of a rush. Count 1,2,1,2,1 and when the fence comes, let the horse come to you. Always look for your next jump! Let the judges know exactly where you are going.
Some apparel that looks good in the equitation ring IMO:
Dark jacket, light shirt. Black or navy jacket with a light colored shirt like the classic white, light pink or blue, or violet or yellow looks good in the arena. For finals though, always go with white.
I personally like the silver stirrup iron (the classic) just because it shows better against your heel, and shows the heel. IMO, the black irons hide your heel, when in equitation, you should show how great your heels are!
These are just my opinions and what I do, that work for me! I have been pretty successful in the AQHA equitation, so I hope this helps! Good luck to you in your finals and competitions!