Here are I do's and don'ts for wedding guests

Guests should vow to be on best behavior at weddings.
SCRIPPS HOWARD
I, (your name here), take responsibility to respond to wedding invitations promptly and to refrain from bringing uninvited guests.
I promise to abstain from wearing white or something too sexy or something too casual, like (gasp!) shorts, and will dress appropriately for the occasion.
I pledge to give a thoughtful toast that is not degrading or embarrassing, but respectful and heartfelt.
Above all, I vow to be a gracious wedding guest, through sickness and in health, from this day forward, as long as I stay on wedding invitation lists.
To stave off unseemly embarrassments, fashion faux pas or other etiquette mishaps, we offer these vows to help renew your position as the perfect wedding guest:
Invitations
Those invitations are sent out for a reason: The paying party needs to know how many people will be attending. Some general tips from the wedding experts at www.theknot.-com:
RSVP is short for, "Repondez, s'il vous plait," which means, simply, "Please respond." That means you should respond either way, whether you're able to make it or not. If the couple has included a response card or postcard with the invitation, it's easy: Just send the card back, saying you will or will not attend. "Regrets" or "Regrets Only" means that only guests who can't make it need to respond.
Respond as soon as you get the invitation. The couple needs a final head count no later than two weeks before the wedding. And let the hosts know if you must cancel at the last minute; don't just not show up.
Don't assume you can invite a date (unless it says "and Guest") and/or bring along your children or other family members whose names are not explicitly included on the invitation.
Toast tips
What's a wedding without a touching toast or two? Some do's and don'ts from Peggy Post's Wedding Etiquette:
The best man gives the first toast. It's perfectly fine for his to be the only one offered. Often, both fathers offer welcome toasts to each other's families and guests. The maid or matron of honor and other members of the bridal party may propose toasts, and the groom may toast his bride and new parents-in-law. We say the bride should toast her husband and new parents-in-law as well.
Everyone should rise for the toasts to the newlyweds except the bride and groom, who remain seated. If a toast is directed to the bride only, the groom rises; if it is directed to their parents, both the bride and groom rise. They do not drink a toast to themselves.
Wedding toasts are best prepared ahead of time, as you may be more nervous or emotional than you might expect. Keep what you say short and to the point -- the spotlight should be on the bride and groom. This is not the time for long stories and humorous anecdotes.