Attire for wedding guests can run the full dress code spectrum, from resort to formal. Check the invitation and wedding website for a hint as to how to dress for the big day. If neither of those spots states a dress code, let the time and location of the wedding be your guide. If you're still in doubt, you can inquire with other guests about what to wear.
Most of the time, it is perfectly fine to dress in resort or semi-formal attire for a daytime wedding. A sundress with a wrap to cover the shoulders and sandals (not flip-flops!) is fine. You could also opt for a nice pair of slacks, a button-down shirt, and a lightweight jacket, with or without a tie.
For a church wedding, a knee-length or tea-length dress is appropriate. Chances are, you should have your shoulders covered inside any house of worship. A suit or nice pants, shirt, tie, and a coordinating jacket would also be suitable.
An evening wedding is generally more formal, and the invitation should state how to dress. If not, ask someone from the bridal party if you are expected to dress in formal or semi-formal attire