Hi there,
Like CJ said, there is no definite guide to such a thing. However, here's a small guide to the things you need to do (and in what order, imo):
a) Learn 68000 assembly. CRUCIAL! I know lots of people will say 'well, duh!' reading this, but I happen to know a "cracker" (not active anymore) that hardly knew 68k asm!
b) Learn the system. Learn it good. Learn it as much as you can. System timers, OS calls, custom chips, critical memory addresses, interfaces. The works. This is crucial as well, otherwise you'll not know what you're doing! (the aforementioned "cracker" above hardly knew the ST!)
c) Code some stuff in asm. Get to grips with the system and how to access it. Floppy access, special tricks of the hardware, etc. Start analysing other people's code, either soruce code or disassembling stuff. Step through code in a debugger.
Once you practice the above enough, then you'll be doing more than cracking. Cracking will be a subset of your abilities. It will become second nature because a protection is a piece of code. Tricky, devious, yes, but a piece of code. And since a program (game, app, etc) runs in memory in whatever way, then it can be deprotected.
Another point: Get comfortable with your coding/debugging enviroment. The tools more used on the ST are: Devpac/MonST, Turboassembler/Bugaboo, Assemble/Adebug, and last but not least Steem Debug. The last is an awesome tool and helps getting results faster than conventional debuggers (because you can issue breakpoints and mem watches practically wherever you want). Personally I use Turboass/Bugaboo and Steem debug when I'm bored
That's about it. Just remember that
"coding" and "cracking/hacking" are not separate things. One
cannot be a good hacker if one is not a good coder. It's taken us years to reach a point where we can patch a game for hdd and falcon etc. in 1/2 an hour.