I drive/push the car onto a couple of bits of thinnish wood first ( some stuff left over from doing my floor ) so I can get my trolley jack under the car. And never, ever go under a car being supported by a trolley jack.
I have a machine mart 2 tonne already which does just fit under the car but ideally will block the wheels in future (BTW only jacked it up once so far)but keep looking at the machine mart aluminium race jack..