First, think about color. Your girls should be clad in one of your wedding colors, so pick a color that is flattering to most skin tones.
Think about fabrics. Will your reception be indoors or outdoors? Will it be very hot or mild? Are you going for a casual or more formal look? If your reception runs the risk of being very warm, avoid farics like satin and charmeuse as they show sweat easily. Some lightweight and beautiful fabrics for any wedding are chiffon, dupioni, and taffeta. Jersey is ideal for more casual settings, while peau de doie is lovely for a formal affair.
Think about cuts. There is a reason people say, "eat, drink, be married". It's because there will be a lot of eating and drinking and your wedding reception! Don't choose a cut that shows every lump, bump, and food baby. A classic a-line works on almost all figures. If you have a bridesmaid who might be expecting around the time of your wedding, opt for an empire waist for the mama-to-be. This is a more comfortable, bump-friendly option. Although the mermaid style is gaining popularity, use caution. Not everyone looks good in a figure-hugging dress.
Keep budget in mind. If you are buying each of your bridesmaid's dresses, make sure you can afford to do so while staying within your budget. On the flip side, if your girls are responsible for purchasing their own dresses, choose one that won't break the bank. Keep in mind, these girls are already doing a lot for your big day and you don't want to tack on too much of a financial obligation.
Do your research, look at many dresses in person, and make an educated choice. Once you've chosen your bridesmaid dress, try on a sample yourself. That way, you can see if you like the way it looks on your body. It will give you a better sense of whether your bridesmaids will be comfortable in the dress.
Here are a few bridesmaid dresses that I love.