Stretching isn't a favorite part in many bodybuilders' training programs, and it's not mine either! I hate it! Even though I dislike it I make an effort to stretch before, during and after a workout.
Stretching helps blood flow to the muscle in turn emphasizes the pump. When a muscle gets stretched there is more room for it to grow. Try to stretch until warm before your workout, then after every second set or so to keep the blood in the muscle region being trained. This will also help you with your lifting as the workout progresses.
Also, incorporate stretching with flexing as this will maximize blood delivery and the pump you will get will be unbelievable and you will think your skin will break.
Hold each stretch for about 5 - 10 seconds and then release. Be careful not to overstretch your muscle as this will cause injury and prevent training. Stretch smart.
Any questions email me on firstname.lastname@example.org