Where can I get good basic information?

I've been handling and shooting guns for longer than I care to admit, however, most of it's been with shotguns and bolt action rifles. In the last 2 years I've picked up both a Mini 14 Ranch and an Eagle Arms/Armalite M15A2. I haven't shot either one a whole lot. I now understand the basics of the Mini 14 a lot better since finding this board, especially the challenge of accurizing it.

I'd like to better understand what I need to know about the M15A2, including trigger tuning, springs, etc, etc. Is there a good site out there, or a good book I can get where I can learn from the ground up? I don't expect to ever get into doing all the customizing that a lot of guys seem to, since I'm not looking at competition or wanting to spend a ton of money on the gun. I just want to learn what I need to in order to keep it in top condition and/or simple improvements.

Thanks.