For me, it really started when I had no internet for well over a year and a few computers. I thought there must be a way to tinker with the files (mostly client side) as Wemade can do it, so why the hell cant I. Started looking at what matermatical rules given the mobs armours weapons and so on and got the swing of it over a period of time.
Start off with somthing you know how to do, and try and spot the parrerns within the files. Then move onto things like mob files, simple to do yet very easy to screw up.