For one thing, I think that it's important to identify your goal in becoming flexible. If you want to be able to do a split at a party, it's a completely different type of training than if you want to be able to kick someone's face off. I'm going to assume that since you are on a martial arts forum, you want to kick face. What you need to do is a combination of dynamic flexibility drills that help your body become accustomed to flexibility within movement. This retrains your nervous system to stop "tensing up" and inhibiting your movement. You will also need to do some P&F Flexibility drills as well if you want to gain static flexibility at a rapid rate.