MSD

Torque them down when it's still up, then again when it's on the ground. If you don't, you risk having one or two lugs loose and developing a wobble, followed by the mechanical condition known by the technical term, "Oh shit, my wheel fell off." Pull the handbrake if you're changing the rear tire.

I've gone almost 200 miles on a donut at an average of 75mph, but the tire is usually only rated at 63 max, so don't be like me. Do yourself a favor and get a full-size spare.

The most important thing that's been mentioned is that you should never put it on a drive wheel. You will fuck up the differential if you do. With a 14 incher and three 17's, you're going to feel the car pulling a lot at first, but you'll get used to it and subconsciously correct for it quickly.

Although some people swear by canned tire sealants, I feel that there's too much of a risk of a blowout if you use them.

edit: You'll thank yourself the first time you use it if you stop by Auto Zone or Pep Boys and get a 2-ton hydraulic jack (assuming your vehicle weighs less than 2 tons fully loaded. Check the sticker on the driver's side door frame or door and look for "GAWR" or "Gross Vehicle Weight" and buy a jack that exceeds that capacity.)