Get a manual, download as much relavent information as you can, and do it.

If its wiring, find diagrams, print them out, and check what wire does what and goes where using a test light or multimeter. Work out what everything is and go from there.
Mechanicals, same as first line, take your time, make sure you have enough allocated time to complete the task and give it a crack. It things turn pearshaped, ask someone, either locally or online.
I am self taught, if I broke something (gearbox) I would take it apart and have a look at what failed, then put it back together and throw it away. A good way to learn I think, root cause analysis helps with future fault finding etc.
Good luck!