A warm-up is still training
A warm-up is still training. Or at least it should be. It might be “preparatory” in nature, but it should still do something SPECIFIC and STIMULATIVE.
If you’re foam rolling and stretching for 15 minutes, that isn’t a warm-up. That’s foam rolling and stretching.
In my opinion, a warm-up should do as many of these things as possible;
Down regulate to up-regulate: disconnect outside stress from gym stress and signal the start of training.
Increase tissue temp and HR: the elastic properties of muscles are best when warm and an increased HR means you won’t dry heave after your first set of X.
Positional specificity: this is a simple one. Train the positions you are targeting. Be it corollary with your upcoming session or just working on stuff you want to improve. Make it specific.
Get sympathetic: to quote @coach_crush, “get your chili hot” and ramp up your readiness to do the challenging stuff.
It’s easy to get lost in the weeds with all this stuff. My advice is to be sure to keep the goal the goal.
TL;DR - Be specific. Be stimulative.