If you're not trying to reseed your lawn, prevent weeds from even germinating with a pre-emergent herbicide, which is most often mixed into lawn fertilizer. Now's the time to make sure that sprinklers work, not when temperatures soar into the 100s. Check that nozzles are clean, that heads aren't broken and that they're in the right place. They're happiest planted in a warming soil. Just be sure to keep them watered.
Tomatoes get all the press, but peppers are perhaps even more useful and easier to grow.
They get few diseases and produce with less heat, bearing well into fall. There are many kinds, from extra-hot to mild. But put in tomatoes too. Shop for summer flowers. Nurseries are stocked with bedding plants, from asters to zinnias.