When you are using a trolley jack, remember that the car and jack have to roll relative to each other, so don't have the handbrake on. When the car is in the air, apply chocks to the rear wheels and use axle stands as Craig has done in his pictures.
An alternative to making a wooden lifting block is to use a rubber pad on the trolley jack, I use ice hockey pucks as they are very cheap and easy to get hold of.
