"stretching scientifically" by thomas kurz is a very good guide to getting more bendy (with the bonus of some hilarious cheezy photos). I don't know how scientific it actually is, but the routines do work.
as a general guide there are 3 types of stretching, static, dynamic and isometric.
static stretching is what you see a lot of people doing before excersise (touch toes and hold for 10 etc) and is generally not the best for improving flexability, and IIRC stretching like that before excersise increases the risk of pulled muscles.
Dynamic stretching is, as the name suggests, dynamic. swinging kicks to stretch hamstrings, swinging arms etc. this is best done when you are warmed up and your pulse is raised, but before your main body of excersise. do 10-15 mins of running, dynamic stretching, then the rest of your workout. I bet you can find a few instructional videos on youtube. be careful not to over stretch though.
Isometric stretching is like static stretching, but you tense your muscles against the stretch, best done at the end of a workout when your muscles are tired. This is really good for improving flexability, but it's really easy to damage yourself so it's best done under guidance from someone IRL or not at all.
Sun salutations* are a nice morning reigeme to increase hamstring and spinal flexability, if you do it every morning you should see a fairly rapid improvement.
sun salutations, the definiteion varies, here's what we do at my kung fu club:
1-stand feet shoulder width apart, toes pointing forwards, head up, shoulders relaxed.
2-lift your arms sideways to above your head.
3-bend at the waist and put your hands flat on the floor about 1.5 feet (up to 2.5 depending on comfort) infront of your feet, also shoulder width apart with your fingers pointing forwards. relax your neck, keep your back straight and push your arse up in the air to make an inverted V shape (like this, downward facing dog
) You should feel the stretch on your hamstrings, if you don't move your hands closer to your feet. Hold this for 10ish seconds.
4-jump your feet out backwards and lower yourself into a pushup position, lower yourself to the floor then keep your hips down, straighten your arms to arch your spine upwards (like this, the cobra
) you should feel the stretch on your abs. hold for another 10.
5-relax to the floor, do the up part of a push up, then hop your feet in to meet your hands. Straighten your legs to a "touch your toes" position hold for 5 then keeping your hands on the floor, hop your feet out to the position for step 3.
repeat steps 3 to 5 between 3 and 5 times
6-when you get to the end of the final step 5, sraighten up, lift your hands sideways up to the ceiling, look up and relax.
as you improve shorten the distance between your hands and your feet for downward facing dog, and push your body towards your knees a bit more to stretch your shoulders more. And hold all the stretches for a bit longer.
I hope that makes sense and is in some way helpful. good luck!