How do you learn how to do on-spot arrangements on piano?

Question

i've seen a few sites saying you can really quickly, but is it possible?

Answer 1

It depends on you and how much work you are willing to put into it. Previous musical knowledge wouldn't hurt either.

American music (like much popular music today) is based around the same basic musical forms. If you learn the music theory behind those forms, you should be able to build arrangements on those forms quite easily. (The forms of American music are actually quite simple.) You can learn this either from studying the music theory and studying the forms, so you know them explicitly, or from playing the piano and playing many many songs until you know them implicitly. I suspect that people who are really good at this can do both.

Have you ever seen the television show on PBS by Scott Huston (sp?), the "piano guy"? I think his show and courses seem to be a good way to go.