Something flattering to you, not something that you would wear to a club or something like that.

No black unless it is a evening wedding, but you can pull off a black skirt or pants and a colorful top or something like that.

DO NOT WEAR HOOTCHIE or SLACKER CLOTHING. Not sure if you own any, but that is absolutely inappropriate.

Keep it clean and covered. No boobs sticking out, bellies hanging out, etc...

No jeans, no tee shirts, no sneakers.

Clean, pressed, professional clothing works well. If you have a business suit or blouse skirt set, that should work well for the occasion.

No all white, but you can have a piece here and there if you NEED to.

Basically how I do it is if I can wear it to a professional job interview, that would be appropriate for a semi casual wedding.

Best of luck, and if you take pics, post them!