Here is a video instruction on how to setup for the barbell bench press and not injure or irritate your shoulders.
For More Specific Tips Check These Excellent Sources:
Bench Press Extra Tip # 1:
http://youtu.be/vUcjOIZc80c
Bench Press Extra Tips #2 and #3:
http://youtu.be/FkCYHXPIKvA
