>>11115
Well, there's over 200 novels out there for you to read, many of which are available as free PDF downloads (But it's more fun to visit your local book stores). There's also the sourcebooks too, which detail the 'Mech designs themselves, as well as the rules for the game. Most hobby shops sell battletech box sets for beginners to try out as well. Plus, there's all the video games. Plenty of genres to choose, but you'll need DOSBOX for some of the older ones.
The lore stretches over so many centuries that you can really just pick any point and jump right in. Personally, I'd recommend picking up the Warrior trilogy of novels, or the seven book Twilight of the Clans series. Anything written by Micheal A. Stackpole is probably well written, but most Battletech novels are pretty quality.