I basically only have novices, so for them it's simple.
Whatever was your last work weight for 5s, that is your opener.
On squats if your opener is under 100kg you then go +5kg for your 2nd, and +5kg for 3rd. If over 100kg, then +10, +10.
On bench it's +2.5kg for each attempt for the women, and +5 for the men.
On deadlift it's as for squats.
Obviously we vary for individuals but those are the guidelines.
My lifters typically end up with 8/9 with this. I like aiming for 9/9, success has momentum.
Sometimes my lifters ignore me. B had done 71kg on bench in a previous meet, she wanted to hit 72.5kg at Nationals. She did 65 which she got, then 72.5kg. She said, "I want to have 2 chances to do 72.5." I explained that she was more likely to get 72.5 if she went 65, 70 and THEN 72.5, than if she went 65, 72.5. Because success has momentum. She ignored me, got 65 and then failed twice on 72.5.
A while back there was an article where the writers had looked at a bunch of meet results, more than 10,000 lifts. They went statistical. And they said that if the person failed their first squat attempt, 1/2 the time they went on to bomb; if they failed their 2nd, 2/3 bombed. The squat in particular I think you need to be conservative with, since it's the start of the meet and everyone's so nervous, lots are lifting at this site for the first time, have never used a monolift before or been judged, etc. Luckily PL meets are fucking slow and so by the time they get to bench they're no longer nervous, just bored. Still, bench seems to see the most bombs, I think many coaches and lifters don't appreciate you don't have as much in you for bench as for other lifts. Then by deadlifts it's "sprint to the finish" time and they can really smash it.
The idea is to create a situation where the person keeps succeeding, this pushes them along and they... keep succeeding.
