ROFL! Thanks guys, you've really cheered me up after what has been a crappy morning so far!
bunker, despite the amusing nature of the replies there is some truth there. You need knowledge of how the equipment you are tuning/fixing actually works so that you correctly analyse the requirement and thus determine the solution. You then need to be able to actually do the work required.
Many become 'air smiths' simply through experience, by tinkering with equipment and maybe drawing upon other's knowledge. Some also/alternatively attend manufacturer's training courses, thus gaining the required knowledge.
Then there's the Honorable Order of Air Smiths and Lapdancers, but since you obviously don't know the secret handshake, I can't tell you about that.