Wait until the hard freezes are over. In the Lawrence area that's usually mid to late April. Turning a system on too early risks cracked pipes and a damaged backflow preventer if a cold night follows.
Open the main water valve slowly. Opening it all at once sends a surge of water and trapped air through lines that sat empty all winter, which can crack fittings or pop heads off their risers. Give the system time to fill.
Check the backflow preventer for leaks or cracks, and make sure its valves are in the right position. Many cities also require periodic backflow testing by a certified tester, so check your local rules.
Run each zone and walk it. Look for heads that are broken, tilted, buried by grass, or spraying the sidewalk; soggy spots that point to a leak; and dry patches that aren't getting coverage.
Finally, reset the controller. Spring lawns need less water than midsummer ones, so start with shorter run times and increase them as the weather heats up. If a zone won't come on at all, it's usually a wiring or valve problem worth having looked at.