Wow... you don't know how to stretch your hammies... ok then. Actually, most people don't really know how to INCREASE their flexibility at all. I've found the best hammy stretch is to lie on the ground on your back, one leg flat on the floor and the other in the air, loop a towel around the raised foot and pull it towards you. Keep a very slight bend in the leg so you don't aggravate your tendons in the back of the knee. If you're doing static stretch hold it for up to a minute. Or you can do PNF stretching, which is where you stretch for 10 seconds, then push back on the resistance (creating isometric tension in the muscle) for 6 seconds, then pull the stretch a bit further and hold for another 10, then resist again for 6, and finally pull back a bit further again for 6.
The way to INCREASE flexibility is to hold the stretch for longer than you usually would, and try and do them maybe 2-3 times a day. You should achieve rapid improvement if you're disciplined in this. Don't forget to also stretch your glutes, hip-flexors, adductors and quads. Often, hammies may feel tight, but it's another group of muscles that are too tight and pulling on the hamstring. Finding the right balance is key in injury prevention.
