When the invitation arrives

RSVP by the card's deadline, or within a few days if there isn't oneIt is especially important to RSVP to a wedding by, if not before, the RSVP date. If there is no date, be sure to respond ASAP, and never later than 2 weeks before the wedding.
Respond in the format requestedMost weddings utilize a digital RSVP these days, but if you receive a pre-stamped reply card, fill it out and pop it in the mail.
Check exactly who's invited before assumingLook to the inner envelope of the invitation to see exactly who is invited; if there isn't one, the outer envelope is the next place to look. Don't add a plus-one or kids' names if they aren't listed — that's a hard no.
Tell the couple who your plus-one is, if you have oneIf you have been given the option of a plus-one, it's polite to let your host know the name of the person you are bringing.
Read the invitation's time and wording to gauge formalityA daytime wedding ceremony and reception often indicate a more garden-party feel and attire. A late-afternoon or evening ceremony and an evening reception are often semi-formal or formal weddings.
Book hotel and flights early if it's out of town if out of town weddingRoom blocks at the wedding rate fill up fast during peak season (June–October), so lock these in as soon as you RSVP yes.
Request time off work right away if weekday wedding or travel needed

In the weeks before

Order a gift from the registry, timed to arrive before or shortly after the weddingThere's no fixed formula — a typical wedding gift can range from $50 to $150+ per person, depending mainly on your relationship with the couple and what comfortably fits your budget — so go with what's right for you, not a strict per-plate math.
Pick an outfit that matches the stated dress codeFor black tie, men's attire is tuxedos — though full tails and cummerbunds aren't required — black bow ties or standard ties; for anything looser, match the general formality rather than guessing.
Avoid white, ivory, or anything that reads as bridalOne of the few true rules left; it's about not competing with the bride, and it's not optional at any formality level.
If you're in the wedding party, confirm fittings, rehearsal timing, and any costs you're on the hook for if in wedding partyShoes, hair, travel.
Sort out a ride home or a room in advance if there's an open barDon't leave this for the night itself.

Lock in your headcountIf your plans change, tell the couple immediately; catering and seating numbers get finalized close to the date and can't flex at the last minute.
Pack the outfit, card, and gift (or gift receipt) togetherSo nothing gets left behind.
Check the weather and venue surface and pick shoes accordinglyGrass, sand, cobblestones.
Map the venue the night beforeEspecially for rural or destination spots with weak cell signal.

Arrive 15–30 minutes before the ceremony start timeSeating generally stops once the processional begins, so cutting it close risks missing the actual vows.
Silence your phone before you sit downAnd hold off on photos if the couple has asked for an unplugged ceremony.
Sit on the side you'd traditionally sit onOne per family, unless told seating is open.
Stick to the seating chart at the reception even if you'd rather sit elsewhereThose charts usually reflect real thought about family dynamics and headcounts.
Hand off your card or gift at the designated table, not directly to the couple mid-receptionSo it doesn't get lost.
Pace your drinkingThis is someone's major life event, not a bar crawl, and a rough night here tends to live on in other people's photos and memories.
Stay through the toasts and first dance at minimum if you need to leave early

Send a thank-you note or message within a few weeksEspecially if your gift hasn't been acknowledged.
Think before you tag or post photosSkip anything unflattering or from private moments unless you're sure the couple would want it shared.