Start small, with only the basic components, and take the time to analyze a simple one already written. I have found some info online about fugues when I was studying it, but none more helpful than the class, I took. So, if you cant take a class from a living teacher, study from the deceased by analyzing what they've already done in a piece. I do it all the time for transcribing solos and things like that. I had to transcribe an atonal tone poem written by Anton Webern one time, and I got so much of a better understanding about how he thought, by doing it. When I wrote it down, I realized this dude, wrote the song based on notes that would spell out his initals once he was done. I have yet to read that in any book about hime. God Bless