It varies from electric co to electric co but a typical process would be this:
You will need to have the building staked out at a minimum, some EC's require that footings are in the ground. Contact the EC and request a new service- depending on what you are putting in the garage a 100A should be adequate. They will take your personal info and charge you a fee (around here it averages $250) They will give you a work order number and schedule a day for the Engineer to visit the site (you may or may not have to be there but it is a good idea) to determine distances for the primary and then secondary, and figure whether you are coming in over head to a mast on the garage or underground. (Underground is always better if you can) If you already have a house on site the secondary can probably just run from there. All EC's have different distances they will allow for no cost to the owner. Once the field Engineer has accessed the site they will schedule a crew to pull the lines.
Typically you will run conduit in to the site when you put the drive in (if you are going underground. If you are going overhead it will depend on distance from the nearest transformer whether you need another pole or they can bring the secondary right to the structure.
If you are running temp service to build the garage you will want to have your temp panel there and the meter socket installed. The EC will put the meter in and hook it up.
Call your electric company. Most of them have pamphlets that give you all of the necessary info you need to install a new service.
