I'm very careful when driving up onto my ramps, and even so, only a month ago I ran a little too far over them and they tilted up... and then when I released the brake the car ran over them and off the back side. BANG. Oops. I wasn't under it, but it was an embarrasing reminder.

Most quality car ramps are great for service under the car. For things in the middle of the car, like exhaust or transmission work, I find that placing them under the two left or right wheels is helpful. I've also got a medium sized floor jack with enough lift to get the car onto the ramps if I need to. That's a big plus, since it's tough to get enough room for the rear to drive up onto them. You can drive up onto one front one, then jack under the rear axle or trailing arm to lift the rear wheel, then place the ramp under that tire.

CAUTION with regards to lifting any RWD Volvo by the rear wheels!!!
The parking brake is all that's keeping you from rolling away when you lift the rear wheels. Raising ONE wheel negates the effect of PARK or leavign a standard trans car in gear- you NO LONGER have anything but the parking brake to prevent it from rolling away. Or at least till it rolls sideways off the jack and gets back on the ground. Ifyou lift under the center of the differential, which is OK, you now have NO means of keeping the car in place. ALWAYS chock BOTH opposite wheels. Note that if you lift the back end, and only chock one front wheel, then turn the key to check something, your car can move because now the steering is not locked. BLOCK THE WHEELS!
As for lift locations, the center of the front crossmember is also good, but make sure the jack is on steel and not 1/2 on the plastic splash guard. Either side frame rail behind the front wheel is a strong location. The factory jack points are good, unless the car is starting to get rusty. Then use extreme care. In the rear, the frame in front of the trailing arms is usually strong but be aware that some brake and fuel lines are in the area. Always double check your jack placement before lifting. Some locations will benefit from a block of wood on top of the jack. Others like the differential, fit nicely into the saddle of the jack and are better lifted without anything on the jack.
One last tip: loosen lug nuts on the ground, then jack the car up. Don't remove them, just break them loose so you're not applying lots of torque while it's in the air. Same when lowering- install and snug the nuts, then lower the car and torque.

Please be careful and get a professional to work on the car if you don't have the equipment to do it safely!
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Rob Bareiss, New London CT ::: '87 244DL/M47- 221K, 88 744GLE- 202K, 91 244 181K, 88 244GL 145K