If the birds are not drinking all of the sugar water, I would suggest emptying and refilling with fresh nectar every other day. Be sure to remove your feeders if you live in a cold climate, just before the first frost. If you do not do this the hummers may not migrate as they should. Since the food supply is still available, they may stick around to eat, and not get out of the area in time for winter. The natural flowers and shrubs you will plant to attract the hummingbirds, will die off as the weather gets colder, allowing them plenty of migration time.
Hummingbirds love red or orange colored, trumpet shaped, single flowers.
This floral shape makes it easy for them to insert their long beaks into the flower and gather natural nectars. They also love Salvia, Fuchsias, Snapdragons, Bee Balm, Nasturtiums and Hollyhocks. These can be planted just about anywhere including window boxes, which will make your bird watching easy from inside of your home. Also, hummers need water. A small pond or container pond will entice them to visit your garden.