Be sure to place different types of bird feeders, smaller and bigger. This way, all those species that come to your garden will have enough room to feed.  If you want them to come back be sure to offer good-quality treats, of course, not the most expensive ones. Good quality means those that meet their nutritional needs. Plus, be sure to always place fresh water for them, as they will for sure appreciate it. If, besides all these, you also clean their area every time you need to, then they will return. Practically, you offer them everything they need.