Battery:  Whenever you are doing anything electrical (unplugging, plugging, etc), always remove the negative battery lead and leave it so it is touching nothing but air.  This is very important when arc-welding.  This protects the computer and electrical system from very expensive damage.  If you have the Theftlock enabled on your radio, make sure you know the unlock code.

Jacking (See the Jacking Page for more info.):  Before jacking, always apply the parking brake, put it in gear, and chock in front AND in back of the tires that will remain on the ground.  Car should be on a solid, even surface, especially if you have a rolling jack.  With your typical rolling garage jack, the jack comes up at an angle, and is going to pull your car a bit toward the handle.  After setting the car on the stands, re-adjust your chocks, as it may have moved them a bit.

It isn't the safest thing to put the car up fully with 4 stands like a short lift, 2 ramps at one end would be better.  If you want to do it, chock the rear, jack up the front, set it on the stands at their lowest setting, jack up the back to the final height (keep an eye on the front stands if your jack "tilts" as described above, you may have to compensate a tad by rolling the jack a CM or two after jacking a bit).  Put the stands under rear, lower it onto them, then jack and stand the front again to match.  Putting the front all the way up first is more risky when you jack up the back, the front stands could tip over.  If you are jacking up to more than like 15 inches, I'd even add a couple more steps, the more gradual, the more safe.  Again, this isn't the most recommended way to evenly jack up your car.  Lower it using the same method.

Stands:  If you don't use jack stands, we'll see you on this year's Darwin Awards.  See the Jacking Page for placement.

Before you crawl under:  I just let the jack out enough to sit the car fully on the stands, then close the valve.  If a stand gives way, you've got the jack there too.  Check your stands to make sure they are sitting flat, then go to work.

Tools:  This is a generic warning, be freaking careful with your tools.  If the tool is new to you, take it easy, and go slow.  With rotary tools, always wear goggles, they toss bits and pieces (of their blades sometimes) at very high speeds.  A bit of metal in the forehead is a good story, a piece in the eye is a bad memory.  Same goes for pretty much any power tool when working with metal or plastic, even a drill can drop shavings in your eyes.

These are just a few tips, always stand back, think about what you're going to do, and think about where it can go wrong.  Then make sure it can't.