make sure you're around when the money changes hands.

choose the key of the song by how your voice pitches, rather than what chords you can play - there are always ways to simplify accompaniments and play it with the chord shapes you know. If need be - have a more experienced guitarist to figure out the chords for you. Sing to him and let him tell you what your keys are.

Buy a tuner that lights up - so you can see it on a dark stage. only put cheap batteries in - else get rechargeables - although really good tuners like the intellituner turn themselves off.

buy as good quality an instrument as you can afford, but be aware there are a few rotten rogue expensive instruments out there. If it feels ugly - it probably is. Get an instrument that YOU like - no matter what anybody else tells you.

always get a hotel if you're too tired to drive home, but don't leave your guitar in the car - always unpack - no matter how tired you are - no exceptions to this.

take out quite a few credit cards before you quit your regular job - getting credit as a musician sometimes isn't as easy.

Never dismiss a technique or a style that you can't feel sympatico with. There is stuff to be learned from absolutely everybody - even other beginners! In fact particularly at the start when you are all tackling the same problems. But later on it is easy to close your mind to a style you don't admire - we've all done that. Narrowing of the mind is the first steps towards getting old. Fight it!

all the best.
Big Al