While frozen fruit isn't always a perfect substitute for its fresh counterpart (there's no way to approximate real strawberry shortcake), in many recipes it works every bit as well—if not better! For instance, since fruits like peaches and mangoes are usually packaged pre-sliced, it means less prep work when you start baking. Also, frozen fruit is reliably high quality because it is flash frozen right after harvest. And if you're making biscuits or scones, which require cold dough to rise tall and flaky, using frozen fruit instead of fresh can help keep the temperature down.
Beyond that, all it takes is keeping in mind a few simple rules of thumb to get the best results from frozen fruit every time. First, remember that fruit is mostly water to begin with, and when it is frozen it adds even more moisture. Because of that, frozen fruit is usually heavier than its fresh equivalent. To prevent frozen fruit from sinking in a dough or batter, toss it in a few spoonfuls of flour or cornstarch before stirring it in.
Alternatively, you can let the fruit thaw, rinse it, and pat it dry before adding to the recipe. (This process also helps prevent dark fruit, like blueberries, from "bleeding" and staining a whole cake or tray of muffins.)
For the same reason (extra moisture), when you're using frozen fruit as a pastry or pie filling, it's also a good idea to bump up the amount of thickener you're using—about an extra ¼ to ½ teaspoon per cup of fruit.
Of course, a colder batter and pastry may also take a bit longer to bake, so you might need to add a few minutes—say 3 to 5—of cook time to a recipe if you are swapping in frozen for fresh fruit. Just keep an eye on things and adjust as you go.