Think twice before you ask.
Once you've asked someone to be in your wedding party, you can't go back. So while it may be tempting to ask all of your favorite friends to be in your wedding party the minute you get engaged, don't. Take your time. Give yourself at least a month, if you can, to mull over the options. Then ask yourself this question: Will I be just as close to this person in five years as I am now?
Ask yourself, "will I still be this close to her in 5 years?"