Don't let your elbows flare out. The style of benching where you aim to "work the outside of your pecs" is horrific idea if you plan on keeping your shoulders healthy. There are other exercises you could use to help you isolate parts of the chest. So when you bench, think like a powerlifter and tuck your elbows in.
This will not only save your shoulders, but will also give you some beefy triceps.
Get your feet flat on the floor. Squeeze your shoulder blades together and get your back flat against the bench. Let your lower back maintain its natural arch.
Tuck your elbows in tight to your body as you lower the bar. Touch the bar on your lower chest, then press the bar in a straight line on the way back to the starting position. Think about stretching the bar as you press it up.