Every 2-3 months I really try to switch up my workouts. This way you make sure you are working different muscle groups and at different angles, making sure you become well-rounded.
Today I am just about to start a 6 week program. If you want to check it out and even try it out - it's here!
http://www.bodybuilding.com/fun/jim-stoppani-six-week-shortcut-to-shred.html?mcid=youtube
This is the workout I'm just about to do:
Real motivation, real work ethic, unreal results.