Wedding fashion tips for a guy?

I'm a young guy and I've never bought a suit before, but my girlfriend's brother is getting married and I think it's time to bite the bullet and get one. Any tips on how to go about buying one? I'm also wondering about shirt and tie colors. I was thinking about a black suit with an emerald or scarlet shirt, but I'm undecided on a tie color. I'm open to any and all ideas, so any advice would be great. Thanks!