Guests wondering what to wear to their first gay and lesbian wedding should remember two things above all: it's just a wedding like any other wedding you've attended, and relax and wear something that makes you feel comfortable. If you are stressed, ask a close friend or member of the wedding party to do some gentle asking for style guidelines.
If your lesbian friends are planning any sort of themed wedding or have style expectations out of the ordinary---say, jeans, black tie or everyone in tropical fashion---they will likely communicate this to you on the invitation or in person. Mostly, your lesbian friends want everyone to have a good time and celebrate their wedding day. There are some general tips to keep in mind, such as: don't upstage the wedding couple; try to blend in with the style of other guests invited; dresses should be cocktail or long, nothing too short; choose pastel colours or basic prints as these look best in photographs; keep make-up minimal, if you wear any, and put hair up for outdoor weddings.
Outdoor or Casual Weddings
Casual or outdoor weddings definitely call for a more low-key style. Gentlemen should wear a suit; seersucker is always a nice choice for an outdoor summer wedding. Make a splash by accessorising with funky shoes or wearing plaid trousers and a suit jacket. Younger couples will definitely have a different sense of style than older couples, so be mindful of the average age of the crowd likely to be invited and plan to blend in. Women looking for a casual option can wear a summer dress and sandals or heels. Your lesbian friends will understand if you don't like feminine apparel, so queer women---or straight ones---will look sharp in a pantsuit. Black is not the best choice of colour for an afternoon wedding, so try beige or cream, or accessorise a black suit with a lighter coloured dress shirt.
Formal lesbian weddings call for a slightly less playful version of the casual summer options. Dresses are always acceptable for women, as are pantsuits or even tuxedos. In general, cocktail length or long dresses are both great choices, so long as they don't show an inappropriate amount of cleavage or look too runway trendy. Don't wear something so outrageous or elegant that you upstage the couple getting married. Women should stick to a dress or an elegant pantsuit, though you can introduce fun fabrics like velvet, if you like. If something formal like a tux is required wear, the invitation will note this. Most importantly, wear comfortable shoes.