An interesting theory on stretching-
This is super important, but it isn't like this is a breakthrough epiphany.
-Duration: This is really hard to say, some people say that less than one minute is utterly useless, others say that more than one minute doesn't do much. What I've been doing: either doing it for one minute or for as long as I can without being in excruciating pain holding a particular position.
-Constant Pressure: Don't jerk around when you stretch, do things slowly and don't let up. If you feel pain, slowly let back the pressure, if you freak out and spring away from the pain you can damage something.
-Strengthen the outer muscles: A nice quote on this subject, "An important fact about stretching, which most people neglect, is strengthening the outer muscles while stretching the inner muscles. You should not only stretch, but strengthen the muscles which are on the outer sides of the muscles being stretched. For example, if you stretch the hamstrings or the back of the thigh, you should also exercise to increase the elasticity of the thigh itself. This is the case because the muscles only posses one function - contracting. Some people think the muscles have two functions pulling and pushing. This notion is false and it is the reason why the outer muscles need to be developed to a point where the stretch can be most beneficial."
Breathing- Take a deep breath and slowly exhale while stretching, relax muscles by focusing on breathing rather than stretching.