your first and best stop for this information is your power company that will - hopefully be supplying your power needs.
They will determine what amperage service will be available to you and at what cost. Normally they are OK with your verbal needs, but may want to see power budgets to justify anything over 200 amp service, or multiple service drops on the same property or bill.
Once the supply is OKed, they will then tell you what size conduit, depth, gnd, sweeps, etc. - IF - "they" allow you to do it, on their behalf. Often times they will ask you to plant a stake where you want the service stub - and they do the work, for a price or ...
It all depends.
Where I am, in TN, they have a 3 page simple drawing of what they expect completed. In my case I simply asked for a second 200 amp service to my garage. I trenched from the garage to the pole stake they specified, I planted the conduit, per their drawing and prepared the ground rod and layed it in the trench. Apply some red tape to the entire ditch and across it at regular intervals and I was done. They were there two days later to plant the pole and tie everything in. Done in 4-5 hours.
In VA, you picked up the phone to Dominion Power and they sent an engineer out to assess and design. Gave you an invoice for the install, which included the minimum charges for that service and once paid, scheduled the install. 3 months later the service was trenched and completed to the garage.
