Just take each house, open it up and clean it out so that it is ready to accept a new nesting pair. We find that the same pairs seek the same house out each year to make their nests and birds do have "favorite" houses. Our most popular bird houses are the ones that are up on top of a post. They are well away from branches and the ground making it more difficult for predators (racoons, bears, snakes) to reach the nests.
Also, you will want to scrub your birdbaths with bleach and water and make sure you've scrubbed away any scum buildup that may have occurred over the winter.
And, same for the feeders. Our feeders really got a workout over this winter and we continue to feed the birds throughout the Spring so that they can focus on having their young and not having to worry as much about food sources. It's important for the health of the birds that the feeders are clean and well maintained.
Enjoy. You'll hear the tender chirping of young birds in a few weeks.