Part 2 (which really should have been part 1 because its more of an overview and less specific)

The Cardinal Rule of being a groom is this: Stay the frick out of the way. Be interested, but not TOO interested. Convince her that you're excited about the wedding, but give her space to do her thing. Essentially your bride's entire life has been spent dreaming about and planning this one day, and before you even popped the question she knew that she wanted green bridesmaids' dresses and a bouquet of white roses. I'm not even kidding either. While you were off daydreaming as a kid about making the diving catch in the end zone and wining the Super Bowl, she was trying to figure out whether she wanted fairy princesses or white unicorn ponies to act as flower girls at her wedding. Any attempt by you to get in the way is going to throw a wrench in her plans, so just stay out of it. You are an accessory, not an integral part of the wedding. YOU are replaceable, black pocket-fold invitation envelopes and monogrammed custom-made table runners are not.
However, a delicate balance must be maintained. If you get TOO hands-off in your wedding planning duties, you will be accused of "not giving a crap about the wedding". This is EVEN WORSE than trying to help and inevitably screwing something up, because when you're messing everything up you're at least making an honest (if not insanely incompetent) effort. If you don't give a crap, it makes her seriously wonder why she decided to marry you, since any rejection of the wedding or anything it entails directly translates into a personal rejection of her. You don't care about the guestbook? Well screw you then. She'll find someone who does.