Be very careful when you lift each end because a trolley jack can cause the car to move forward/backwards and it could come off the stands very easily.
This is a very important point. You want your trolley jack to move rather than the car when lifting the second end. Make sure the trolley jack is longitudinal with the car and free to roll on the floor. I sometimes used a sheet of ply on the floor to provide a smooth surface for the jack.
The bigger the trolley jack, the less pronounced this effect is, as the radius of the arc through which the lifting pad moves is greater.
