People often come to me and tell me that they have been performing routine exercises to keep themselves flexible. Oddly enough they often report that inspite of their efforts they still feel very stiff.
One reason that is often overlooked is that they are actually trying to stretch the wrong area/tissue. If you want to improve flexibility, whatever your particular strategy, you need to stretch the correct area.
An example: People often try to stretch their hamstrings by putting one leg on a stool and then bending their heads down towards their knee. When you bend forward you are actually releasing the pressure on the hamstrings as you use the flexibility in your spine to get your head closer. If you want to stretch one area (and this is not always the case) then it is best to localise your stretch. To get the hamstrings you can first keep your back straight and push your shest out to remove all spinal flexion. You then put one leg on a stool and then lean forward like you were a waiter bowing (this is only one of the many ways to stretch the hamstrings). You should worry less about how far you go and more about where you actually feel the stretch. You wil get mostly the hamstrings if you leave your foot relaxed. You will get the calf muscles as well if you pull your foot up towards you. Further load can be applied by turning your pelvis/hip/leg so that everything is kept square and there is no where else that can give way to relieve the load on the hamstrings. I could give you more variations but this would be a could starting stretch.
Add some relaxed breathing, sustained holding and a bit of patience (repeating 3-4 times for 10 + seconds ,3-4 times a day)and over a few weeks you will feel your hamstrings getting looser.
The important thing to remember is that if you don't feel a stretch in the right area when stretching then you aren't really stretching…
Good luck with your health and fitness.