My first advice is to get a coach (not a personal trainer!) who has competed, and competed WELL. I’ve seen waaaaay too many typical commercial gym PT’s try to get clients ready to compete, and just drop the ball horribly. Of course I’ve also seen “coaches” who have competed, and while to someone who doesn’t know any better that may sound good, but the last thing you want is someone who has routinely placed at the very bottom of whatever contest they’ve entered.
Next, find someone with a proven track record. This is the current generation of “I can quote studies and make myself sound really knowledgeable online.” As such, make sure someone knows, and has shown that they know HOW TO ACTUALLY IMPLEMENT the information you need in achieving a contest level physique. Something Brad (@BrickHead) and I joke about whenever we see certain other coaches subtle bragging about whatever degrees they may have in an attempt to throw shade at anyone else, is how you really only need the most rudimentary UNDERSTANDING of basic nutrition and how it factors into performance and appearance in regard to bodybuilding. Most of the really sciencey stuff I’ve learned over the years never comes up, and Brad’s an actual RD with MULTIPLE sports nutrition related degrees -lol
Lastly,… BE HONEST with yourself. No one needs a zillion cheerleaders constantly praising you, because when you finally get up on that contest stage, and you get a brutally honest assessment of how you stack up against other competitors, it can be a very shocking and rough pill to swallow if you realize that everyone was just being supportive in the worst possible way (even if not intended as such).