I roll my wraps up first. I keep my knees locked and my quad flexed while I wrap. I usually rub a block of chalk on the area to be wrapped to prevent slippage.
I start about 6 to 8 inches above my knee cap leaving a short bit of wrap hanging loose. Then I work my way down, pulling all the stretch out the wrap with each turn and overlapping each turn about an inch.
Just below my knee cap, I start my way back up. I lay a couple turns around my knee, leaving most of the remaining material to wrap around my quad/hams.
I then tie the end to the tab of wrap I left at the beginning in an overhand knot- leaving little rabbit ears of wrap material. This is little different than what most folks do. Most lifters will tuck the end under one of the turns of the wrap. I always thought this was a pain in the ass to do and it makes the wrap prettty hard to get off. With the tied method, you just pull one of the ends and the wrap pretty much just pops off your knee. This is real nice, especially when you have a painfully tight wrap on.
I feel like the most effective wrapping involves really pinning the lower part of the hamstring to the bone. If done right, this pretty uncomfortable- but well worth the pain. I don’t waste any wrap below my knee- it really does not give much support there.
Also, in a contest setting, there is a limit to how high and low you can wrap- six inches either way from the knee cap as I recall. However, if the wrapped area doesn’t look long, then judges are less likely to question how high the leg is wrapped.