As best man, you may think you’re just a glorified groomsman, but guess what? You actually have special responsibilities — you’ll be a combination valet and hand-holder as you help the groom come through this nerve-racking experience with flying colours.
As leader of the groom’s posse, you’ll:
Serve as the groom’s personal aide and adviser before and during the wedding. This can include helping him pack for the honeymoon (the valet part).

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Help the groom choose and rent (or buy) wedding formalwear, and coordinate the other groomsmen’s rentals. You guys are supposed to match, after all! You may be expected to arrange accommodations for out-of-town groomsmen.
Organize the stag party. Don’t be shy about enlisting other groomsmen to help you out — most guys don’t mind this duty! Put financial worries out of your mind — the cost should be split among everyone who attends the bash.
Attend the rehearsal and rehearsal dinner with the bride and groom and all the other attendants. This is your chance to figure out how you’re supposed to walk down that aisle.

Stand beside the groom at the altar and keep the bride’s ring until vows are exchanged. Find a safe place for the ring (and triple check that your pockets don’t have holes) — you don’t want to fumble around when it’s time to whip it out.
Corral the other guys and make sure they’re performing their groomsman duties.
Sign the marriage license as a witness after the ceremony, along with the maid of honour.
Give the officiant a sealed envelope with his or her fee (the groom’s responsibility) just after the ceremony.
You may be announced with the maid of honour when the reception begins.

Dance with both the honour attendant and the bride during the wedding party dances.
Give the first toast to the bride and groom at the reception. This is your biggest — and probably most frightening duty
Decorate the getaway mobile. Grab the other groomsmen and the bridesmaids for this one.
Drive the couple to the wedding-night hotel or airport after the reception. If you perform this service, you’ll need to stay sober throughout the reception. If you have a feeling this may not be possible, hire a limo to drive the couple into the sunset.
The wedding will be over in the blink of an eye, so remember to enjoy yourself at the reception. After all, you’re there to celebrate the happiest day of your best friend’s life.