The Novus cleaners are the easiest route for basic cleaning. If you want to get much better results you should go with wet and dry paper, starting with basic fine and working your way finer until you can then use a good quality cutting compound like G3 to polish. If you're feeling really brave, you can clean them thoroughly and then use an oxy/cet flame to flame polish them. This will give a perfect glass like new finish. However, it certainly isn't easy. I completely destroyed the first one I tried. In the end, I just kept using it to practise on until I was happy with the results.

Have fun.