There’s a bit of a divide whether or not you should stretch before working out. Personally, I don’t. If you’re going to go through complex motions with your joints, I don’t think it’s best to stretch out your muscles beforehand.
Warming up is a good idea, of course, as is stretching after exercising. I never stretch when I enter the pool or the gym, but I do some ten laps of slow swimming or get on the stationary bike and make sure to not skip a step in my twenty-minute post-workout stretching program.