I have been learning myself. The best way I have found is to download a minimal theme, like Jive for instance, and play with the settings in the .rc files. Head over to o-t-s at Sourceforge
http://o-t-s.sourceforge.net/. That is the homepage of the OTS2 standard. It describes _exactly_ what structure to follow.
Go to the loose screws repository
http://loose-screws.com/index.php and download a bunch of modules. Pick one that enables a feature you like, start at the top of the readme file and step by step add it to your theme. Again play with the settings to see what they do.
Comment _every_ section you work on. Unless you have a photographic memory you will loose track of where you put things. Read all of the posts here, and on the chatboards of every LS related site you can find. Some really interesting ideas come up, and most of the questions you will come up with have been answered before. There are some very experienced people who post on these boards, including module authors.