Rule #1 NEVER get under a vehicle supported only only a jack (I think we can all agree on this one) Rule #2 Shake the vehicle, lean on it, put it to the test with whatever you have supporting it. This includes jackstands, lifts, ramps, etc... Rule #2.5 if only raising one end of the vehicle, block the front and rear of the other axle, on AT LEAST one wheel. I will admit to being a little lax on #2 because I lift the same 10 or so vehicle models/platforms every day, and I know exactly where to lift them on a twin post lift. I equate rule #1 to one of the cardinal rules for firearms: don't point the gun at anything that you don't want to destroy, don't put anything under a car supported only with a jack that you don't care if it gets destroyed. The more supports you have to back up what ever you have supporting the vehicle the better.