Warm-up Sets - how does everyone else do it?

[Buddy_Christ]

this is something that i didn't need to worry about on my old routine because i did 4 sets of every exercise, increasing weight and dropping reps each set. that gave me 2 warm up sets and 2 work sets essentially. but now warmup is becoming an issue on my 5x5 routine. my partner missed 5 reps on his first 2 sets of seated OHP yesterday, he only hit 4 reps, but the last 3 sets he hit all 5 reps. myself, i get better/stronger as sets go on as well, but it's too early into the 5x5 routine for us to be getting into this situation, and i'll be there soon myself if my warmup doesn't change.

currently what we'll do for 5x5 exercises is 12 reps, 10 reps, then 8 reps, increasing weight each set, then we'll jump into 5x5, but even then, my first 2 5x5 sets are starting to become a little shaky as i go up in weight. what i'm thinking is that during our warm up, the last warm up set should be a heavy set, maybe a 1RM, then drop into 5x5.

i do stretch before we hit the weights and between sets to keep everything moving and keep myself going good.

any suggestions? the reason i'm thinking a 1RM before the 5x5 movements is because we're not working our max weight on 5x5s. so far it seems the only thing i don't even need a warmup for is deads. all my fatigue lifts, however, i don't need warmup sets for, as i'm already pretty "warm" by that point.

sorry for the long post about something this simple, but since everyone is different in how their body responds, it might not be very simple. i figured i'd give as much info as possible to get the best suggestions.

thanks for any help you guys can give me!