Last weekend I was at a meet in Dayton, OH with my long time friend and training partner- Joe. He crushed a 700lb squat at 198 in wraps, hit a 413lb bench, and fell a little short of expectation with his deadlift. He left with a PR total at 1720 and PR squat and bench, so really it was a great day, just shy of a perfect day. I'm proud of his effort and resolve. He'll get his deadlift figured out after some tweaks and more time under the bar.
The one thing that I was blown away by were squat warm ups. It was a monolift meet and they had one mono in the warm up room. Joe brought a PVC pipe with him that had his bar height measured for squat and bench. I don't go that far myself- I know exactly where the bar needs to be by chest height. But this is a great idea, and a lot of guys will even do it with a tape measure.
Everyone did a fair job of working together, which is always nice to see. But not one lifter knew their rack height, and half of them didn't even care. From 135 to about 80%, most lifters would even let me change the height for them- "Naw I'm good."
I'm not one to coach guys on meet day unless there is something blatant that can be fixed quickly and easily. So I wasn't about to give a clinic on 'how to warm up on meet day.'
But long story short...
#1 Know your rack height whether you do it by tape measure, PVC pipe or broomstick, or knowing exactly where it needs to be on your chest before you get under the bar.
#2 Treat every warm up like you're on the platform. Get the mono height set. Get under the bar just like it's your first attempt on the platform. And execute the lift.
#3 Take the warm ups that you need. If 225 is on the bar and you need 135, ask for it and take it. Don't skip weights because you're not comfortable speaking up or asserting yourself. It's your day. Everyone will respect that because we've all been there before. And if someone is a dick about it, they're in the minority and they're wrong.
These are also all lessons for training to some degree. Good luck.