You need to find relatively cheap ways of improving your knowledge not only of paintball markers but of engineering and electronics in general.
If you see a bargain knackered gun on the classifieds then buy it and try and fix it, once you are familiar with that type of marker you could help out anyone who has a problem with that type of marker.
Remember there is a great deal of responsibility with teching someones beloved paint slinger. If you knacker someones gun you have to pay to fix it, regardless of whether that involves buying them a complete new gun.
You are also responsible for your own destiny, if you do a good job word will spread about what a good job you did, if you mess up everyone will know and people will be reluctant to hand over their guns to you.
Tom is a great example of word of mouth, Im sure he wont mind me saying he hasnt been paintball teching all that long, but he is already regarded on this forum as one of the best angel techs. Everyone I talk to who has had their gun serviced by Tom sings his praises.
This is due to his engineering knowledge and attention to detail.