Here is some wedding guest etiquette I have picked up from family members, websites, friends, and personal experience as a not-so-good wedding guest.
Definitely
If the invitation says your name “+ guest”, you’re only
supposed to bring a date if it is someone you are dating. The bride and groom should have met the date
you are bringing or at least know your date’s name. A +1 invitation isn’t an opportunity to bring
a random person so they can get drunk with you, even though it’s tempting (and awesome). If you’re bringing a date just to bring a date, you’re just
costing the bride and groom money and guaranteeing a guest they don't know appears
in the background of all their wedding photos.
Unless you know the bride and groom really well and know
something specific they want or are super-crafty and can make something
amazing, it is really appreciated when guests buy wedding presents off the
registry. Brides and grooms register for
items for a reason (probably because according to movies you get a scan gun at a Bed Bath and Beyond and get to go wild and it’s awesome), so help ‘em get the stuff
they want and need. Plus there will
always be older guests who don't shop from a couple's registry, so if you’re under 60 and can
use a computer, you should do so. Even
if you find it pretentious that your friend who
can’t cook now apparently needs two stainless steel cherry-pitters.
Probably
Most wedding guest etiquette guides say that a guest should not wear white to a wedding. This is probably a good idea so as not to upstage the bride, but a cute white eyelet dress with a cardigan or a man wearing a light seersucker suit could be appropriate at a casual summer wedding.
Depends
A wedding guest etiquette tip I have read recently says to refrain from posting Facebook photos of a wedding until after the bride and groom and their families have posted some and that doing so is like "scooping" the married couple on their big day. Tons of people post facebook photos of a wedding even while the wedding is happening and, honestly, the bride and groom won't get to see their official photos that were taken by a paid photographer until weeks after their wedding, so they may appreciate getting to see a few candid pics their friends took at their wedding in the meantime (also they will be on their honeymoon anyway, so shouldn't get too mad).
Wear