Before installing a permanent irrigation system, you’ll need to:

See if your locality requires a building permit.
Check for underground utilities before digging. Before you begin any excavation (that means even digging a hole), you’ve got to call and check for underground utilities. This isn’t just a good idea, it’s the LAW. Call your local utility company for information.
Research your local municipal watering ordinances.
Because any of the above may become an issue, always check your local building codes before starting an irrigation project.

In order to purchase the right components, you’ll also have to determine your own specific:

Water pressure in pounds per square inch (psi).
Water meter size (for a municipal system) or well pump size (for a well).
Water service line size.
Water flow rate in gallons per minute (GPM).
Type of backflow prevention required by local code.