Dig down, getting rid of all organics. Get rid of the topsoil. You need to get down to the 'dead' subsoil. Reason? Organics decompose, settle, and over time will cause your patio to settle. Also, organics retain water and can swell/shrink as they wet dry. Bad in winter when retained water freezes and heaves the patio. Organics will also promote vegetative growth, and you don't want a sapling sprouting in the middle of your patio.
Grade the subsoil so it is flat, well compacted, and pitched away from your house. Minimum is 1" of pitch every 6', max is 1" every 4'. For a 12' patio the surface should slope between 2" and 3" down and away from the house.
Yuo need to contain the patio. This often depends on how deep you had to dig to get to subsoil. You need some kind of border around the perimeter to keep your patio materials from migrating into your yard. You can use pressure treated lumber, commercial plastic edging devices, or a poured concrete footer.
Place landscaping fabric down over the subsoil. This will act as a barrier to prevent the stonedust from migrating into your subsoil. Then place stonedust over the fabric. Stonedust is, essentially, finely crushed stone. Totally inorganic. It compacts and binds very well. It drains very well, too. Build the stonedust up to the final level of your patio less the thickness of your surface material.
Example, you excavated 7" to get to subsoil and you're using 2.5" thick pavers. Lay down 4.5" of compacted stonedust. Yu may need 5.5-6" of uncompacted stonedust to get 4.5" of compacted stonedust. You can cmpact it by renting a plate compactor for an hour or use an 8" square tamping bar. After compacting you should be able to walk across the stonedust and not leave footprints.
Now it's time to lay your surface material. Geometical bluestone? Randon flagstone? Or the easiest, concrete pavers. Pavers ar ethe easiest and most economical, and they also come in myriad shapes/sizes. Your design will likely result in you having to cut some pavers. You can rent a mechanical breaker or use a saw.
You can now broom sand over the pavers, working the sand into the cracks betwen the pavers. Then, if you still have the plate compactor, you could run it over the pavers one last time. Optional.
Get yourself a chair, a bottle of wine, and sit back, relax, admire your work.