Why does my car judder?

Maybe you’re in the wrong gear?

when does it judder? all of the time or just sometimes?

Perhaps your wheels need to be balanced.

If it’s shaking when you’re rolling, have a mechanic look at the tires, the wheels and the brakes (or, less likely, the shocks and suspension bushings). If it’s shaking when you’re still but the engine is running, have a mechanic look for misfiring engine (clean/replace the spark plugs or wires, change air filters, check fuel filter). If it’s shaking when you’re still and the engine is off, check for earthquake or possibly large radioactive lizards stomping nearby.

in addition to rob’s suggestions, you might also want to check the engine mounts to be sure you havent broken one