Stretching is probably one of the most important parts of a work out and definitely one of the most neglected. People see it as a chore and want to jump straight into their heavy sets, wasting no time, but let us tell you something- ample stretching is your insurance policy against injury and can actually lead to further growth and stronger muscles.
With the correct stretches practiced with proper form, you can unleash a new stimulus for your body. You can lengthen muscle heads, improve flexibility and joint health, improve posture and much more. Count light warm up sets as part of stretching too as this gets the blood flowing into the targeted muscles of your current workout.
Stretching in between sets should not include bouncing, but instead aim for slow controlled movements. This is referred to as static stretching and should be done for all major muscle groups, this can make muscles look harder and fuller also.
When train a particular muscle group, aim to stretch the antagonistic body part, so if training biceps you will stretch your triceps which helps deter any muscular imbalances.
Another common method?
Bro science often tells us that everything should be done to the extreme, we all know that this is not the case but with stretching, intensity can sometimes be good. This is for advanced lifters who know how to listen to their body, beginners should avoid this to avoid injury.
An extreme stretch would involve contracting the muscle and holding it for 30-60 seconds, this will hurt a little and should be done slowly. If done correctly, studies have shown this to increase hypertrophy and IGF-1.
So stretch, warm up and do what you have to. Your gains are not going to build themselves.