I'm no expert, but I've learned a bit from trial and error. You need to have a chawan (or at least something bowl shaped, with a flat bottom), and a whisk (ideally a bamboo one made for the purpose). For the powder I use a scoop - about a flat teaspoonful, I'd say. The water should be boiled and then cooled to around 80 degrees. Pour an inch or so into the bowl, and whisk it quickly for a good thirty seconds - that should get rid of the sludge. It should froth up to an extent.

It is fairly bitter, and I can see it wouldn't be to everyone's taste, but I love it.