A couple of years ago, I was asked to do the sound for a band I knew - I'd never done it before and made my first mistake by thinking "how hard can it be"! Fast forward to today and I can honestly say that every gig is a learning experience. I've acquired a nice range of kit to the point that I'm now providing complete sound packages for four bands - keeping me busy most weekends.
The best investment I made was a one-to-one training session with Howard at Basesound. Self-teaching is fine, but it's no substitute for learning from a seasoned pro with decades of experience. Howard patiently took me through the fundamentals and taught me many important techniques, routines and disciplines which I use every time I'm setting up or stood behind the desk. Amazing how much you could do in a day! The biggest endorsement I can receive is to have members of an audience complimenting the sound, and I put that down to Howard's teaching. I will certainly be back another day to take my development further, but whatever level you're at, get yourself to Basesound, you couldn't spend your money any more wisely!