When learning what to wear to a backyard party, keep in mind that there are no rules that say you have to dress differently depending on the time of day. However, it's fairly typical for afternoon parties to be a bit dressier. Think floral blouse with cutoff shorts, a cute sundress, or sleek trouser shorts with a graphic tee. Once night rolls around, you'll want a good layer to combat the chill, so be sure to bring a denim jacket, cardigan, or shacket.