I just started being a guitar tech in 2004. After seeing and having so many bad guitar techs over the years, I learned what not to do. Having good relative pitch helps. It's a job that is as hard or as easy as you make it.
Advance planning and regular maintenance lessens your panic moments to a manageable few. I look at it as being a good butler...when you walk on to an empty stage, it should become "more empty'. Stealthy professionalism is the way to go. There are a lot of tasks that are best performed before the gig, rather than on your knees during a performance.
Military design is the way to go. Overbuild everything because there are other things to worry about during a performance than equipment (like tuning.) Stretching strings until they no longer go flat means they won't go flat during a performance. There should be three wraps on the post of the tuning machine so there will be enough down bearing on the nut, otherwise the string won't sustain or stay in tune properly.
Gear on the road gets a lot of wear and tear, so maintain gear like you would a car that gets that much use.