It really depends on the game/platform, but getting used to using a reverse engineering tool and a debugger is a must. If you can, use IDA, I'm stuck with Ghidra for now but most of the time I have to work against it to get stuff done. Even with C output you'll still need to get used to working with assembly to hook stuff, and do other code modifications. (You can use a library like detours, but when things start crashing it really helps to know exactly what every piece of your code is doing.) Also imgui/nuklear really help with getting a nice GUI for your mods early on.

Though tbh the best thing you can do is just pick up a game you like and just have a go at reversing it, it'll be a bit slow but the more you reverse the easier it gets. After you reverse it it's just a matter of looking up each topic (ie dll injection, hooking, etc) as you need them. None of them are that hard, they just seem overwhelming if you try doing them all at once.