Unfortunately, tutorials in data file "hacking" (i.e. recognizing and decoding data from game files) are not very detailed and quite rare, and you'll find tutors even rarer. But what it all boils down to is simple logic, recognizing recurring patterns and being good at programming/graphics/3D/whatever subject the data you're trying to decode belongs to. A good starting point is "how would I store this data?", and that means the better you know the subject, the more accurate your assumptions will be.