Trying to do different things at shows just leads to problems.
Do remember that (even if you have been able to school over the jumps earlier in the morning, but especially if you haven't) horses are more apt to run out or stop at jumps when at shows than at home. So, without getting the horse running crazily or anything, do be attentive on each approach to the first hint of lack of straight/forward.
That is a wide open question and I assume you are talking about riding the same 4 year old horse you discussed in your other thread? I think this is the third thread in three days? It will be easier if you keep one thread going and follow up with it. It is impossible for us on a forum to give riding/jumping tips to someone we have never seen ride nor seen their horse. I won't go into the whole issue about jumping a 4 year old horse. I think you mentioned in the other thread that you were taking lessons and working with a trainer? If that is indeed the case then that is your go-to person for show ring tips, general riding tips and show grooming tips.
Personally, jumping a horse at 4 is asking for it to be lame by the time its 6. Trainers in Europe dont even start thier horses under saddle until 4 or 5, and they dont start jumping until the horse is 8 to 10. Many European horses are still showing into thier late teens because of this. Dont try too much at once with your young horse. It will burn him/her out at an early age. Ive seen them get rather nasty attitudes by being pushed to hard and too soon.