I use a 3 ton floor jack and 3 ton jack stands.
I jack the car up under the factory jacking points. I then place the jack stands under the frame of the car, and voila.
I also always keep the floor jack raised so that if by chance the thing falls, the floor jack will keep it from crushing me.
And when the car is raised, i make sure to shake it and rock it to see if it is stable. If I have the slightest hint of movement, I dont get under it until it is solid.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.