What I try to do is find out in advance what kind of equipment they will be using, tables, balls, and especially which cueball. I'll then find the local pool room that has that type of equipment and for at least a week, I'll put in 2 hours a day minimum, playing the ghost.
Rest is very important too. I try and get a good nights sleep the day before a big tournament. Tournaments can be long drawn-out affairs for many reasons and I want my mind/body to be sharp all day.
One other small thing I do is watch videos of the players I admire in tournament conditions. Not so much for how they play the game, but how they conduct themselves in that environment. Learning to win and lose with class will help you become more successful in the big tournaments.