Here are a series of video links with Strength Coach Mark Rippetoe. Coach Rippetoe discusses and demonstrates the proper technique for a Bench Press. Take a look:
http://www.youtube.com/watch?v=UwQyFoD6E80&feature=channel
http://www.youtube.com/watch?v=SQutODgl2J4&NR=1
http://www.youtube.com/watch?v=iMq1rTaErMc&feature=channel
http://www.youtube.com/watch?v=GmM9yxbYLc0&feature=channel
