Wedding attendant: a person (regardless of gender) who is selected by a couple to participate as an honored guest in their wedding celebration.
When a couple asks you to be in their wedding, it is more than just buying a special outfit and going to extra parties during the journey to their wedding day.
In fact, in the past, being an attendant was quite dangerous in some cases (check out this awesome article: http://mentalfloss.com/article/57821/21-historical-roles-and-responsibilities-wedding-party).
The couple chose you because they love you and want to make sure you are there to surround them with love as they solidify their union.
But, you are also there to help out, and there are some easy things you can do to make the couple's day easy and special.
The last time I was a wedding attendant, about four months before the wedding, I hit a major financial brick wall (single mom, deadbeat boyfriend draining my time/energy/money, master's program, teacher's salary = perfect storm) that was making it difficult to honor the wishes of my friend to stay at the winery where she was having her wedding. I called her and told her I couldn't afford it, and that I would find another place to stay and just drive in. We got in a HUGE fight about it. Money is tight around wedding time, for everyone, in some cases.
In hindsight, I should have just asked my parents for help, or asked her for other solutions. I learned a lot from that experience, as well as a lot from watching other situations as they happen during the 55 weddings I shot in the past 2 years. This is what I know will help make the day smoother:
Know the vendors
Ask the couple who they have as their vendors. Attendants of honor, in particular, can take a minute to introduce themselves as they encounter vendors, and have a helping attitude or role as a liaison to make sure the couple's wishes are met.
You will be photographed. Act natural, don't ham it up for the camera, and keep your face happy. Others will follow your lead resulting in great memories for the couple.
Leave the drama at home
Got a partner who always makes you feel like shit? Having a hard time with your job? Leave the partner at home (and really, break up with them - no one deserves that), and forget about work for a day. If the couple asks you about anything that could turn into a long saga of complaints, keep it short, and then redirect with something related to the wedding. You can pick up your regularly scheduled friendship venting sessions in about 24 hours.
Be on time
Okay, sometimes you get a flat tire and your lateness is excused. Other than an extenuating circumstance though, be ready early and happy to sit around and wait if needed.
Lay off the booze (a little)
Weddings are celebrations and often include copious amounts of alcohol (at least for us in Wisconsin). I encourage this. However, an attendant who cannot keep their eyes open, or keeps running off (and stalling the progression of the day) because they are too drunk/high/whatever is not okay. Keep it together until the dancing starts and imbibe responsibly.
The couple getting married should be doted on. Not in an overly-demanding way, but if they need something, offer to help. If uncle Fred is monopolizing their time during the reception, take one for the team and distract him with The Twist. So many times a couple is left to manage difficult situations while attendants look on, adding to their stress and detracting from the enjoyment from the day. An attendant who helps deter that is a friend indeed.
See the story about my attendant fail above. Sometimes the couple wants us to do things outside of our normal realm of comfort. Obviously, if something violates your fundamental values, say no and explain why, and try to come up with a solution - or respectfully back out of the role. However, if it is that the couple asks you to wear your hear in a top-knot or buy a set of weird cuff links...just do it. Sure, you may not like it, but it won't hurt you.
More importantly than my silly list: talk to the couple. Ask them what they need from you. Ask them questions about their wedding day. Listen to what they say. Consider their feelings on this important day. As long as you are kind, compassionate, and loving, you will be the best attendant they could ever ask for.