Declining an offer to be maid of honor is a very difficult task. Knowing that a bride gives considerable thought to who she will ask to be her maid of honor; and knowing that she makes her decision based on who she trusts the most; saying no becomes a sensitive matter. Decline the offer gracefully, and only if you really can't fulfill the duties, despite your good intentions. You must avoid making the bride feel rejected and emotionally unsupported.
Be honest. Decline the offer from the start if you feel you're not up to the task. Don't keep the bride hanging on a decision. Waiting on your decision makes her unable to move forward with other tasks that involve the maid-of-honor. Telling her upfront saves the bride valuable time, as she can start looking for a replacement right away. Plus, you are being more considerate and fair to her if you say no as early as possible.
Provide a valid reason for declining the offer. The maid-of-honor is a position of high esteem. Almost no one would actually decline it, knowing what an honor it is to simply have been chosen. Therefore, you must tell the bride why you can't accept the position. Whether it's because you won't be able to skip work on her wedding day due to a very important project, or because you can't afford to host the bridal shower or bachelorette party, a sincere reason would be very much appreciated.
Offer a sincere apology for saying no to the offer. Avoid hurting the bride's feelings and creating a possible rift in your relationship. Tell her you feel honored and you honestly wish you could accept the positionut -- but you can't.
Offer to help. Show how much you wish to be involved in your friend's wedding by asking how you can still be of help, even in a different capacity. This shows your friend how much you really care for her and her groom.
Make sure you check on the bride every once in a while, to demonstrate your honest concern for her. Show her that you are still the best friend she can rely on, seek advice from, be excited with, and who offers a listening ear for her rantings during this emotional time in her life.