The most important thing is to first determine who you are truly closest to. Ask yourself these questions:
- Who would you call if you had a question or need help with a personal problem?
- Who has been by your side when you needed them?
A true bridesmaid is someone you have history with. This can be a tricky task if you have lots of close friends or if you have been in all your friends' weddings. Don't feel you have to ask someone to be in your wedding unless you honestly feel that she is one of your closest friends.
It's always nice to include siblings, either on your side or your fiancé's side, but it's not mandatory (note: ask if your mother feels strongly about this first).
Another thing to consider is the size of your wedding. If you are having 200 people, then five to seven bridesmaids/groomsmen will work, but if you have 30 guests, a smaller bridal party makes more sense.
It's totally OK to have someone of the opposite sex on your side. You can always mix up the girls and guys so no one feels singled out. And don't forget: If you are maxed out on your bridal party, there are other roles you can give close friends such as readers or ushers.