There are two key components to safe and effective benching, especially when you get heavy:
Problem is, many times it's difficult to get enough friction between your back and the bench to apply these two tactics. After a rep or two, you find your shoulder blades slipping into a more protracted position, or even worse, you find yourself slipping toward the uprights. That's a shitty way to celebrate International Bench Press Day.
Head to your local sporting goods store and get yourself a can of adhesive spray, the kind athletic trainers use before they tape an ankle. (Mueller Magic Grip Spray is one brand to look for.)
Spray the upper portion of the bench where your shoulders will be before you lift. You'll be amazed at how well you can wedge yourself in before you unrack the bar. Minor shoulder issues often suddenly disappear, and new PR's often appear out of nowhere.
This spray won't damage the bench or discolor your clothing. In fact, you'll probably need to re-apply the spray every 3-4 sets. Give this simple trick a try and I'm betting you'll never bench without it again!