Step 1. Decide what you need.
Step 2. Multiply that by 1.5 - 2.0
Step 3. Shop for a high quality two stage, or a two piston oil crank
compressor if you only need a small one.
Step 4. Consider used, as you can sometimes get a killer deal on a big one.
Step 5. Install it right, electrically, piping, and air dryer.
Step 6. Enjoy and use, knowing you won't fry it, overwork it, or have it
fall short when you need it the most.
My observations from not following these steps.