PNF (proprioceptive neuromuscular facilitation) stretching is one where muscle group is passively stretched, then isometrically contracted against resistance while in the stretched position, and then is passively stretched further on. Basically, it is a combination of passive and isometric stretching. PNF is the most effective currently known way to increase static-passive flexibility.
Although PNF stretching is possible to do on your own, the most effective and the simplest way is to stretch with partner’s assistance, who provides resistance against the isometric contraction and then takes the joint through its increased range of motion.
Most PNF stretching techniques employ isometric agonist contraction-relaxation where the stretched muscles are contracted isometrically and then relaxed:
After assuming initial passive stretch, the muscle being stretched is isometrically contracted for 7-15 seconds, then the muscle is relaxed for 2-3 seconds, and then immediately stretched again (even further than the initial passive stretch) for 10-15 seconds. Rest for 20 seconds before performing the next PNF stretch. You can repeat the stretch 3-5 times.
There are PNF techniques that use isometric contraction of antagonist muscles where the antagonists of the stretched muscles are contracted.
The only difference from the PNF technique described above is that instead of the final passive stretch you isometrically contract antagonist muscle for 7-15 seconds. Some people like to make the technique even more intense by adding a passive stretch after the antagonist muscle isometric contraction. Although this can be more effective, it also increases the risk of injury.
Myofascial release is a muscle relaxing technique where you roll something (applying pressure) on a tight muscle. Traditional static stretching works on tissue length, while myofascial release (other similar techniques) stimulate golgi tendon organ which controls muscle tissue tension and can cause it to relax. You can roll your tight body area with a barbell, use a foam roll under your body or anything that you can roll on, as long as you apply pressure on the targeted muscles. Roll for around 30 seconds or longer per tense muscle group.
If your muscles are tight you should include dynamic stretching and/or myofascial release to your warm up routines after cardio prior to resistance training in order to increase your range of movement on compound exercises. If you do not have any issues with muscle tightness and flexibility than just cardio warm up is enough.
Static stretching is more effective in increasing flexibility than dynamic stretches or myofascial release, however it reduces muscle power output. For that reason static stretches should be performed only after resistance training. If you avoid post resistance training stretches then after a while flexibility suffers. Other than improving flexibility, static stretches done at the end of your training session quicken muscle recovery and reduce DOMS (delayed onset muscle soreness). Also slow, relaxed static stretching is useful in relieving spasms in muscles that are healing after an injury (pulled muscle).