Comment by alberto-m

From my brief experience, it seems that reversing old games is one of those disciplines where there is no good step-by-step course. One can start learning some theory (I did so by reading “The Art of Assembly Language Programming” – if I had more time, I'd try “Reverse Engineering for Beginners”) but then one has to get his hands dirty. Real-life games are typically not simple, but one usually just needs to reverse some small parts to produce new interesting modifications.

But surely reading tutorials is useful to learn techniques and tricks. I recommend this article to start: https://www.lodsb.com/reversing-lz91-from-commander-keen (not totally for beginners, but very friendly, and it can help to get used with the jargon). I am also publishing war stories on this topic on my blog (marnetto.net).