That could be a long answer.....
The place i'd start is by ensuring you have a reliable backup, because theres nothing worse than being rendered unable to play due to your latest experimental tweaking going awry, and trust me on this it will, regularly, so have one gun that runs well and promise yourself you wont fuck with it unless it breaks down, took me too damn long to learn that properly
Second thing is decent tools, seriously takes a lot of ballache out of working on guns, no real formula here other than if you use it a lot its worth getting a good one. Good hex drivers are invaluable for working on aeg's (and screwdrivers and torx bits). Same goes for workspace, a proper table, good lighting and a comfy chair are very much reccommended (also work mats, pots for storing screws and covering up all those nooks and crannies that are black holes for those springs that go sproing help too)
Apart from that its a case of just do it, more experience helps. There's loads of advice out there on the internet, youtube guides can be great for identifying those not so obvious steps in dissassembling something. Sadly disseminating the good info from the bad is a minefield and ultimately you'll end up making mistakes, buying the wrong parts, etc, nature of the beast.
If you take the time to learn, experiment, figure out how these things work then it can be quite rewarding, but i'm not going to say it wont be strewn with dissapointment and financial hubris.
