This is a good question. Of course, you want to hit that fine line between warming up enough, but not wearing yourself out.
When I plan my numbers for a comp, I plan the opener really light, the 2nd attempt as a small PR, and the 3rd attempt is to go for broke. So, what I do is start with 25s, and work up in 25 # plate incremement until I get to where that 1st attempt would be my next logical jump. If I want to pull 430, and I'm attempting 375, 415, 430, I would warm up with 95, 135, 185, 225, 275, MAYBE 315. I might also do some band good mornings to get the erectors flooded with blood and oxygen without actually working them.
Just what I do...