Early spring offers a moment to make minor repairs to the lawn; major lawn renovation is best left until September. Patches of bare soil can be cultivated and seeded for spring, but expect seedlings to wilt and possibly die once summer heat sets in. Areas of the lawn often die back from shade or poor drainage and may be best converted to garden beds for ground covers suited to those conditions.
It's time to put down pre-emergent crabgrass killer, unless you are trying to get grass seed to germinate. Corn gluten provides an organic alternative to crabgrass killer and gives the lawn a spring nitrogen feeding at the same time.