I usually do some light weight mobility stuff with my shoulders and back before a bench session to get the blood flowing and get the muscles warmed up. I also usually throw in some bodyweight squats or leg extensions, seen some folks tear some low body parts while benching. I used to just get under the bar and bench the bar, but after going through a few strains, bumps and bruises I've learned to take some time with a warm up (no stretching) and make sure things are done right.