We generally recommend finding a squeeze bottle of some sort (an old ketchup bottle works well), and filling that with one part cerium and two parts water.

Shake it up in suspension and then, as you are working on your piece, just squirt the mixture onto your polishing pad as needed. You'll find that as your polishing pad charges up, you need to add less and less cerium to it in order for it to work well.

You will always need to use some cerium and water with the polishing pads though, even after they are charged up.