Writing songs and submitting them as works in progress to forums would give you quick direct feedback. Are you trying to make a song that's in your head and you want to know how put it down on paper? Take music theory if you haven't, that would be a good start. Taking classes in music theory would be a prerequisite to taking composition classes at a school. I'd consider that instead of going it alone with a book, I think you could even find online classes. You'd end up with a book in the process as well.