ok, you'll want a 20 amp breaker. Check your compressor to see if it's 220 or 110 so you know if you need a single or double breaker. You want 12/2 or 12/3 (again depending on 110 or 220) NM-B wire (avaliable at your local hardware store). Run the wire from the box to the location of the outlet. Wire the outlet. (see below for extra help here) Shut off the main breaker in your box. Unscrew the breaker cover and remove.
If 110:
Your black wire goes to the screw on the back of the breaker. Your white wire goes to the neutral bar (you can identify this by looking for the bar where all the other white wires are going to)
If 220:
Same as above, but the black goes to one of the back breaker screws, and the red wire goes to the other.
For 110 and 220, the bare wire goes to the ground bar (again identifiable by seeing where all the other bare wires go)
Now clip the breaker in - you'll see how your particular one clips in. Reintall the cover and switch the main breaker on.
Wiring the outlet:
assuming 110, the black wire goes to the brass screw, the white wire goes to the silver screw. The bare wire goes to the green screw. I assume this compressor is in your garage, so you will need a GFCI outlet to do this. If this isn't an inspected job, try to find a GFCI that was made before the UL2003 requirements came out. UL2003 GFCI's will automatically disable themselves after a certain number of ground faults, and will require replacement. The older ones will keep working.
If the job is inspected, you're screwed and must get the UL2003. If you're worried about passing inspection, don't. Make sure you do a very neat job - no wires all over the place, especially in the breaker box, and you'll pass unless the inspector's a jerk.
If you want more info, Black and Decker puts out an excellent series of books about wiring. They have a Beginner, Advanced, and Complete book - the complete is just the beginner and advanced combined. Get that one. Well worth the money. It covers pretty much any household wiring job you could ever do.
Also, you didn't mention how old your house is. If it's really old, you may have rubber-iinfused-cotton insulated wires. The rubber breaks down after 25 years and will flake off. If you have this wiring, BE CAREFUL. If you break the insulation off you MUST replace the wire or you risk a fire.
Note (not for you - I know you know this being an electrician, but for others): Any time you are working with electrical wiring, ALWAYS assume the power is on or could be turned on at any minute. Never know when someone's gonna turn that breaker back on while you're rewiring the outlet/switch. Follow the "one hand rule" - only ONE hand touches what you're working on. The other hand touches NOTHING. If you get shocked and you are not following this rule, the current can go through your heart. Also, lift the opposite heel to the hand you're workign with - i.e. right hand, left heel. This will make an easier path through the side, rather than through the middle of your body. Much better to have current going down your side than through all your organs
Never work on wiring with any moisture present - this includes sweat. If it's hot, keep the sweat away from the job. Not only does the water in the sweat increase your conductivity, but the salt does as well.