Hi John,
I've enclosed a link to some blues lessons. Although I'm repeating what Lisa, Light and Christopher have already said:
Simple 12 bar blues generally use the 1st, 4th and 5th chord from the key that it's played in......C-F-G......G-C-D......E-A-B.....Most 12 bar blues use 7th and/or 9th chords along with a 5 note minor or 6 note blues scale:

http://guitartricks.com/tutorial.php?input=158

http://guitartricks.com/lesson.php?input=10888&s_id=399

Doug