You'll likely get a lot of responses on this. Here's what i concentrate on:
Hands shoulder width or slightly wider on the bar.
Control the weight coming down, elbows out.
Keep your back flat on the bench, do not arch.
Touch the bar on your chest, no bouncing! (If you have to arch your back or bounce, you're lifting too much!)
Control the weight back up, squeeze your chest at the top of the lift.
OK bros, am I forgetting anything?