Getting your car in the air is necessary to perform many automotive projects. At first glance it's easy enough to do; place jack under car, depress handle, watch car rise. In reality, there is more to it than that, particularly if you want to keep yourself safe and prevent damage to your car. Obviously this project addresses the B5 chassis Audi A4, but many of these hints would be applicable to almost any unibody automobile.
If you need to get the whole car in the air, I recommend raising the front first. There are a few good reasons for this: First, without removing the plastic undertray from beneath the engine, you can't get at the front subframe (which would make a suitable central jacking point up front, and that would allow you to raise both front tires off the ground at once). You can't get that undertray off of the car very easily with lifting the car--it's a Catch 22. Driving the front of the car up onto ramps would be an acceptable solution--that would allow you to reach the undertray and then raise the car more as needed, particularly if you need to remove the front wheels.
Second, to raise the rear of the car, you can use the rear differential (on a Quattro) to lift both rear tires at once. But once you have the rear of the car on jack stands, you'll have to raise one front side at a time, shifting the weight of the car between the two rear jack stands and increasing the risk of the car sliding off. You can minimize the risk by lifting each front corner a little at a time, but you still have to get one side fully on a jack stand before shifting to the other side.
I've always hated how floor jacks can mar the undercarriage and side sills of cars I've owned. You might not notice any damage from using the jack once, but use it repeatedly on the same spot and you'll end up with scratches and scrapes on a part of your car that is exposed to a good deal of water, dirt, and salt. You can buy replacement jack pads, and of course jacks that have nice, cushioned pads. I've found you can make do with a few layers of paper and a good wrap of duct tape. When the cushion gets damaged or dirty, simply tear it off and tape on some more protective paper. You could do the same with your jack stands, but as the car is stationary upon those, I consider that a lower priority.
As mentioned above, I recommend raising the front of the car first. Another good reason for doing it this way is that the rear tires can be immobilized using the parking brake. However, that is not sufficient to ensure that the car won't roll away when you lift it up. Place wheel chocks as needed to prevent the tires from rolling.
The tool kit in your trunk is really only for roadside emergencies. Get a real floor jack, jack stands, and lug wrench before you tackle anything more than changing a flat tire. Having said that, the tool kit does contain a small flat-blade screwdriver and a curled metal hook you can use to remove the plastic center caps on the stock wheels.
I discovered the tool kit's metal hook only after I had already removed the center caps using the screwdriver tool. I was careful not to damage the caps or wheels when using the metal screwdriver, but it would be better to use the screwdriver only to create a gap at the edge of the wheel cap. Then insert the hook tool in one of the holes on the perimeter of the cap, put your finger in the loop and pull the cap off.
Don't worry; we're not removing the wheels yet. I'm just reminding you to loosen those lug bolts slightly before you get your car off the ground. The ground will keep that wheel in place while you apply the torque necessary to break loose the tight lug bolts. Here I'm using a breaker bar on the required 17mm socket to provide ample leverage. Always loosen and tighten lug bolts in a star pattern (every other bolt on a five-bolt wheel). It may not technically be necessary in every circumstance, but it's a good habit to have.
A triangular, indented notch on the rocker panel indicates where Audi would like you to place your jack to raise the car, behind the front wheels and in front of the rear ones. It's safe to lift the car on the raised seam just inboard of this notch, where the jack pad is place in this photo. This is great if you're only changing a tire or doing some maintenance on a single corner of the car, but what do you do when you want to raise the car and then place it on a jack stand?
This plate is plenty strong to support the weight of the car, and the raised center portion is a perfect spot to place your jack pad. Ignore the exact angle of the body of the jack in this photo--the next photo shows the best way to orient the jack as you raise the car.
The one catch, at least with the jack I used, is that I needed to drive the car up onto some small pieces of wood in order to get enough clearance to slide the jack under this lift point. Orient the jack so that you can raise and lower the handle just behind the tire, giving yourself more range of motion.
Place your jack stand underneath the jack point on the standing seam below the rocker panel (as indicated by the triangular indentation in Figure 7). Carefully lower the car onto the jack stand, slide your jack out from under the car and carry it around to the other side of the car.
Once you have raised and supported both sides of the car, you can remove the wheel. Spin the lug bolts off. Because of the use of bolts instead of hub-mounted studs, the wheel can rock a bit when you've removed all but one or two of the bolts. You may need to hold the wheel against the hub in order to remove the last bolts easily.
Here's a good look at one of the lug bolts. If you've worked primarily on Japanese or American cars in the past, these may be a change of pace for you. If you wish, you can replace these bolts with studs and lug nuts--this is necessary in order to install some aftermarket wheels.
Once both front corners are supported on jack stands, you can turn your attention to the rear of the car. If you've got a Quattro, you have a rear differential, which doubles as an excellent spot to place your jack to raise the entire rear of the car at once. If you haven't already loosened the lug bolts on the rear wheels, now is the time to do it, before the tires leave the ground.
Here's a close-up look at the correct placement of the jack pad on the rear differential. Be careful not to accidentally place it on the exhaust hanger just aft of the differential, as this will not support the weight of the car.
Other suitable jack points located at the rear of the car include the raised seam below and inside of the rocker panel (where the jack stand is placed in this photo) and the rear subframe mounting point, which is a circular plate with a bolt in the center and a rubber puck above it.