Frankly, it's a bit overwhelming to a newbie. Which era to play, which house/faction/whatever, which mechs to choose. It goes on and on.
The Battletech website does a pretty good job of trying to get you oriented to the universe with the eras etc. But I've yet to find something as clear as the Flames of War materials on force selection. They have books for this, but the question is, which ones? In this, my third excursion into BT, I'm going to commit to learning the universe from the perspective of the Alpha Strike rules, the Clan invasion period.
With that said I bought two pdfs from DriveThruRPG:
1994 Invading Clans Sourcebook. It's a scanned copy of the original published material. Though it's been cleaned of any errata found since then. Just skimmed it.
The description from RPG:
Invading Clans describes the history, culture, and military capabilities of Clans Smoke Jaguar, Nova Cat, Ghost Bear, Steel Viper and Diamond Shark. Also included is an overview of occupied worlds, deadly new BattleMechs, and eight full-color pages featuring renderings of Clan uniforms and ceremonies.
The other is the much newer Era Report 3052. This is a standard PDF. What I like about this one is that it covers both sides of the conflict. So I can make some inner sphere forces with all the minis i have from the introductory box set. (Remember, if you can't find a copy, don't buy some outrageous ebay copy. It's being reprinted soon.)
The description of the book:
Era Report: 3052 describes the state of the Inner Sphere and the Clans at a pivotal period inBattleTech history: the early years of the Clan Invasion. Presented as a general overview of the period, rather than a focused report on a single conflict, this book includes descriptions of every major Inner Sphere and Clan faction. Notable personalities, military forces, and an overview of the technological capabilities of the Inner Sphere and Clan powers of this critical era in history are also provided, along with special advanced-level rules for campaigns set in this era, whether played using the Total Warfare core rules or those found in A Time of War: The BattleTech RPG.In terms of complexity, or depth, it goes like this:
Alpha Strike rulebook gives a nice quick history of the entire universe and timeline. It then boils down the Clan invasion and forces. Very brief though. 21 pages total. (By the way, then follows a section explaining how to find out more, other resources, etc.)
The Era Report 3052 then takes all the above info and expands more into both sides of the conflict in 100+ pages. It will be interesting to see what else is added above what is shared in 21 pages. I believe there are also tracks to be used in campaign games etc.
Finally, the Invading Clans sourcebook goes into 150+ pages of detail into only the clans. The traditions, army TOE, a couple selected mechs, and a detailed explanation of the significant planets taken during the initial invasion. Amazing detail.
All this given so you can have a rich experience playing a game with big stompy robots.
New to Battletech section on the Battletech website.