1. Before you approach your friend, the bride, really think about the reasons you want to back out. This isn't the time to be indecisive. Make sure you are certain you cannot be a bridesmaid.
2. If you're certain you cannot fulfill your duties as bridesmaid, I recommend having an honest conversation with the bride - the "kiss, kick, push" method. Start with the kiss - metaphorically
speaking, of course! - by telling her how much her friendship means to
you and how happy you are for her. Next, the kick, which is that you
need to back out of being a bridesmaid and why. And lastly, a little
push, by bringing the conversation back to a positive note with a little
nudge towards what's next. It might go like this, You are a great couple and your wedding is going to be
beautiful. I am honored you asked me to be your bridesmaid.
Unfortunately... as I wouldn't be able to fulfill my duties – bridesmaid
dress, bridal shower, bachelorette party, etc. You know I care so much
about our friendship and so look forward to celebrating your marriage
with you as a guest at your wedding."
I'm sure she will be disappointed, but hopefully she will appreciate your honesty. If not right away, give her some time.
3. I think the best advice is to get together with the
bride and really have a discussion with them about why you are backing
The next best piece of advice would be to do it as soon as
possible. The more time they have, the better. Try to find solutions or
listen when the bride brings up solutions.