If you want some extremely effective stretching technique, listen close.
Firstly, stretching for short periods (under 30 seconds) really doesn't stretch you out. It will release basic tightness, but that's about it.
If you want to get really limber and build flexibility, you have to focus on it.
The best way to do that is to stretch as you normally would, to the point of being taut (pick your particular stretch), then flex against it for about 10-15 seconds. For example, if you were stretching hamstrings: put your feet together while you are sitting on the ground and try to touch your toes. Get as far as you can, then grab your ankles or lower leg and (keeping your knees straight) pull back as though you're trying to sit up. Do this for about 15 seconds and you'll find you will be able to stretch much farther than you could when you started.
Pick a good set of stretches of tissue groups you want to stretch out, and do three sets of these. Be warned, just like working out with weights the first time, initially your tendons and ligaments will recoil from being stretched. They will tighted up the next day and you'll notice that you have lost flexibility. If you don't give up, you'll work through that period very quickly, probably even the second or third stretching session. Keep to your stretching routine though and you'll notice rapid advances in your flexibility.