Place a call to your city building department to see if there are any required building permits.
Contact your utility company and have them mark off any areas with underground wiring where you're not allowed to dig.
Measure the desired length and width of your patio and pound four wood stakes into the ground to denote your four borders. Run a piece of twine along the outside of the four pieces of wood.
Excavate a hole within the borders of your area, approximately six inches deep, and level out the soil at the bottom.
Install flexible edging around the inner border of your digging area by pounding posts into the ground to secure the edging.
Dump a three-inch layer of decomposed granite onto the entire bottom surface of your dug-out area, and level out the decomposed granite until it's even.
Compact the decomposed granite down tightly with a plate compactor, which can be rented from a store that sells building materials.
Add a three-inch layer of sand on top of the decomposed granite and level it out by using a rake to smooth the surface.
Lay your flagstones one at a time, starting in one of the corners. If you're using loose flagstones, leave around one inch of space between stones. If you're using flagstone pavers, leave 1/8 inch of space between stones.
Fill in all cracks between the flagstones tightly with sand and spread the sand around with a broom.
Sweep any sand off the surface of the stones, and the patio is ready to use.