Fruit salads should be fresh, vibrant and tasty, but some attention must be paid to the dressing. Photo by Lindsay Turner.
According to Rick Martinez of Bon Appetit, you should think of a fruit salad dressing the same way you think of a "regular" salad dressing, and should make sure that it includes "an acid, a fat and a dominant flavour component". Olive oil works well as a vinaigrette base, and nut oils are a great place to start for something creamier. In either case, you'll want to whisk in an acid (such as citrus juice or a sweet balsamic) and other flavourings like fresh herbs and spices, maybe even some chilli flakes for heat or maple syrup for sweetness. Try to keep things a little sweeter than you would for a leaf-based salad (I would avoid garlic), but don't be afraid to get a little out there.
Once your masterpiece is ready, it's time to dress. If your fruit is good and ripe, wait until half an hour before serving before drizzling it on. If it's quite firm, you can dress up to three hours ahead of time. (For help on choosing which fruits to salad-ify, and when to chuck 'em in, check the link below.)
There Is Such a Thing as a Great Fruit Salad [Bon Appetit]