I come from a boxing background and I like to stay loose, so I will stretch 15-20 minutes before I train quads. I thiknk gorging the muscle with blood is one of the biggest precursors to muscle growth, and the more you stretch the muscle fiber, the more blood it can hold. I start with my quads first, then my hams. Hamstrings are incroporated into a lot of quad movements; if you've ever pulled your hamstring, you know you can't train your quads at all.
Strict, heavy squats are the way to add quad size. Bit you get to a certain point where you have the right amount of size on your quads and you're just going for more sweep and muscle density. Full range of motion hack squats really hit the outer sweep of the qyad.
I always like to make sure I never go so heavy that I can't do at least eight reps, and I try to never do more than 15, unless I'm doing it on purpose.
Since the legs are a very large, dense muscle group, I think it takes many sets to properly work them. i typically do 6-10 sets per exercise, using the first three sets as a semi warm up. I also like to test myself and see how strong I really am and how much I can take. I've learned that doing 6-7 sets really burns my muscles out. I still experience muscle soreness, and I honestly belive it's from doing the extra sets. Precontest, I might do as many as 10 sets of each exercise per bodypart.
I training quickly and intensely, allowing myself only 7-20 seconds between sets. I feel the leg shouldn't be receoved before the next set; they'll have plenty of time to recover when I get out of the gym. Between sets, I shake the muscle out a bit, just to get the blood in there. I'd never advise this pace for begineers or for those wo want to gain muscle mass. In the end, you need to be very instinctive about your rest intervals, just like other training variables. Find what works for you.
I don't lock out at the top of squats and leg presses. Tis takes the muscular straing off the muscle and puts too much pressure on the knees themselves, making the joint vulnerable to injury.
For quad separation, the most important thing is using afull range of motion and really squeezing the muscles. Don't just fly through the exercise; do it at a slower pace and try to hold the weight for as long as possible. I really believe that pulls out the striations and separation.
My quad workout is very basic, but basic works. The exercises I do are pretty much the same for each workout. My legs fee liek rubber at the end, tending to cramp up if I sit down or get in the car, so I move around for about 15 minutes afterward.