From my experience, it's (for the most part) just finding something semi-related to what you're searching for, and tracing it back as far as possible. For instance, you might find the game's entity/game object list by tracing back from something seemingly unrelated such as the ammo in your gun using break points (ammo address -> gun base address -> address in player object -> address in entity list). Obviously this involves a bit of RE too. You might want to reverse functions you land at to see exactly what they're doing rather than just blindly going about.
It seems as if you're looking for some kind of universal method for game reversing though, which you're not going to find. It's about trying every possible thing you can think of to find what you're looking for.