Think British countryside, midi dresses or longer dresses in lighter fabrics. There will be grass—plan footwear accordingly. Hats and all forms of headwear greatly encouraged. Sequins...not so much (unless it is your true heart's desire).
Wear a tie, don't wear a tie, three-piece, mix-and-match...go crazy with it. Given the proclivities of certain family members of the bride, it must be said that guayaberas are emphatically discouraged (sorry, Nimo).