After you get engaged and have a few of the big wedding-planning details decided (such as when and where the event will take place), it's time for you and the groom to think about how many bridesmaids, groomsmen, and other attendants you would like to have and whom you want to ask. Don't wait too long to decide -- you'll appreciate having their help early on.
The maid or matron of honor and the best man are also known as the honor attendants. Traditionally, the sister closest in age to the bride serves as the maid or matron of honor. If the bride has more than one sister, she may ask them all to be honor attendants. If there are two, one can be maid of honor and the other matron of honor, or they may share a title. If the bride does not have a sister, she may ask a close friend, cousin, or aunt. In an especially lovely gesture, some brides ask their mothers, stepmothers, or grandmothers.
The groom typically asks the brother closest to him in age to serve as his best man, but he can also ask more than one brother, or choose a close friend, cousin, or uncle, or his father, stepfather, or grandfather. A bride who is especially close to a brother or male friend may choose a man as her honor attendant; the same holds true for a groom who wants to include a close female relative or friend.
Bridesmaids and Groomsmen
Although certainly not a requirement, it is fitting for the bride to include the groom's sisters and for the groom to include the bride's brothers in the wedding party. It is also both thoughtful and diplomatic to invite future sisters- and brothers-in-law who won't be in the wedding party to participate in other special roles, by performing a reading or holding a pole of the huppa, for example.
A girl between 3 and 7 years old may be chosen as a flower girl, and a boy of the same age as a ring bearer. Children ages 8 to 15 may serve as junior bridesmaids or groomsmen. At a formal wedding, two young children may act as pages, holding the bride's train as she walks down the aisle. And children between 9 and 12 may serve as candlelighters. There is no limit to the number of young attendants, but typically these roles are reserved for relatives and the children of especially close friends.
Number of Attendants
If you're looking for concrete numbers, there is one helpful guideline to follow. When groomsmen act as ushers, the preferred ratio is one for every 50 guests. Many couples will choose the number of bridesmaids accordingly -- for symmetry at the altar and in photographs -- but the number of bridesmaids and groomsmen need not match. The extra men or women may walk down the aisle alone or in pairs, or one groomsman may escort two bridesmaids (or two groomsmen, one bridesmaid). In these cases, it's important to ensure that the aisle is wide enough to accommodate a trio.
For an intimate gathering, one or two attendants on each side may be just right. There may be only a best man and a maid or matron of honor, or no wedding party all -- just the bride and groom walking down the aisle arm in arm. For a larger, more elaborate celebration, a couple will typically want to be surrounded by a big group, in keeping with the mood of the occasion. Four to six on each side is common, but couples are still known to have as many as 12 bridesmaids and 12 groomsmen.
Source: Martha Stewart Weddings