Depending on the lifter (style, gear/raw, strengths/weaknesses), some people get more out of their knee wraps than others. But no one will benefit from a knee wrap, if it's laid across your knee like strips of toilet paper..
When wrapping your training partner's knees, obviously listen to what they want in terms of tightness, and style (how the wrap is laid across the knee), but no matter how they want their knees wrapped, you need to make sure you're taking all the slack out of the wrap as you go around the knee. What I've seen a lot of people do (I probably know 2-3 people that I trust to wrap my knees), is put a ton of effort in pulling the wrap as hard as possible in one direction, but then when they go to make a revolution around the back of the knee, they keep the wrap loose, pretty much defeating the whole purpose of pulling the wrap so tight in the first place. Now with my squatting style (I'm narrower than a typical geared squatter), I get a lot more out of a tight wrap, and if that isn't the case with you, having an extremely tight wrap might not be necessary. This is based off what I know I need to get the best possible carryover for my squat..
SO, here are a few things to keep in mind when wrapping knees:
1) Pre-roll the knee wrap tightly, so as you wrap you don't have to worry about pulling out tons of slack constantly
2) Make sure the wrap-ee keeps their knee straight and quad flexed (and keeps the wincing and complaining to a minimum, faces of pain are not acceptable, only phrases such as "is that as tight as you can go??").
3) Make sure whichever style of wrapping you use, that you don't leave gaps in the wrap. If the person squats and you see skin as the wrap opens up, you left too much space between revolutions (or didn't wrap tight enough)
4) Pull tight and keep tension the whole time! Don't waste your energy pulling one part of the wrap tight then letting the rest get loose
5) Don't be afraid to use chalk on the persons knee and on your hands to help keep your hands and the wrap from slipping
6) Always have a backup wrap handy! (You never know when you might lose grip on a wrap)
Here is a great video of Monster Garage Gym's Eric Maroscher teaching how to wrap knees the right way:
[youtube=https://www.youtube.com/watch?v=8E2W9-3f7qg&app=desktop]
And here is a video of me wrapping one of my good friends Mario (the normal amount of sh*t talking was toned down since we knew we were being recorded.)
[youtube=https://www.youtube.com/watch?v=gRPYhljiRwc]