I'm somewhat new to competitions. I just started entering this year with three under my belt so far. I've been fortunate that I picked up two bronze medals, four golds, and one Best of Show
Here's what I can offer from my experience so far:
1) Don't "expect" anything but feedback. Of course you go in hoping to win, but you don't know your competition and you don't know the judges, so every competition is different.
2) Don't be disappointed by inconsistency. I had conflicting feedback on scoresheets for the same beer. It kind of leaves you hanging on where to make changes. Also, don't be disappointed by inconsistency between competitions. I had a milk stout that I entered in two competitions. Same batch, judged on the same day. In one competition it got a 41 and a gold, in the other it got a 29. The beer that won me BoS scored a 43.5 in that competition. In another, it still scored 40, but didn't place. So, every time is a crap shoot.
3) Plan ahead. I didn't give myself quite as much time as I'd of liked to condition and clarify. I don't think it made a huge difference, but a few points might make a difference in any competition.
4) I paid a lot of attention to water profile for all my competition beers. It was a bit of a pain, but I think it made enough of a difference to be worthwhile, especially with styles like Belgians and lighter beers.
5) Have fun!