The Maid of Honor's responsibilities include:

1. Attending all prenuptial parties.
2. Help address invitations and announcements.
3. Entertain a party for the bride and groom…if possible.  This could be a couple's shower.
4. Assist bride with going away clothes and luggage.
5. Be sure that bridesmaids are kept aware of their fitting appointments, rehearsal obligations and any special duties that the bride may wish for them to do.
6. Arrange with a florist for a supply of rose petals to shower on the bride and groom as they leave.  If a flower girl is in the party, she is responsible to see that the child knows when and how to do this.
7. Arrive at the church,or wherever the wedding maybe, or home of the bride early enough to help with bride and bridesmaids with dressing (at least 2 hours early).
8. Remind the best man which ladies will be wearing their flowers  (Mother, grandmothers, organist, soloist, hostesses, etc.).
9. Assist bride with her train during ceremony and in the receiving line.
10. Hold the bride's wedding bouquet for the exchange of rings during the ceremony and hand it back just before the recessional.
11. In a double ring ceremony, carry the groom's ring until it is time to hand it to whomever maybe holding it during ceremony.
12. Assist the photographer with identification of the members of the bridal party and later for pictures, which are taken at the church and reception.  Be sure to find the kind of candid shots the bride may want of the out-of-town guests.  Be certain the photographer has taken an appropriate number of these candid shots.
13. Witness and sign the marriage certificate after the ceremony.(if applicable)
14. Stand in the receiving line.If there is one.  The traditional place to stand is at the groom's left side with her bridesmaids to her left.
15. Assist the bride when she is ready to change into here going away ensemble.
16. With the best man, help the couple depart.
17. See that the bride's gown is taken care of according to her wishes.  Usually taken to the bride's home or to a cleaner.

 Remember, this is the bride's day.  Your job is to assist the bride and help her day be as carefree and special as possible. As a maid of honor, you should set the tone among the women in the bridal party.  Stay cool and never out shine the bride.  It truly is an honor to serve. 

(this tip originally from Wedding Approved)