Detman101,
I also stepped outside of my introvert box about a year and a half ago and invited myself into our newly formed church praise band. (My interest in playing guitar was revived when I discovered the Avett Brothers, but that's another story). We have some bonifide professional musicians and all I knew was how to make a few chords and strum a little on my old Alvarez acoustic. Couldn't read a lick of music or tell you a thing about music theory. They let me in and I'lll tell ya, it's been a life changing event. They were understanding of my basically being a beginner and didn't really have anyone strumming acoustic rythym. It's amazing how much I have learned from them and how much I have grown in my spiritual life. What a way to worship! (Out of my pulpit now).
I have now performed about 6 times. One of those times was with a piano and myself as the only instruments for one vocalist, so, it goes without saying that my self confidence has benefitted greatly. I also must say that a LOT of hard work and practice got me to where I am today, but the desire to learn MUST be there first. Remember, anything worth having is worth the effort to get it. If you can afford it, take some lessons also. I've been taking lessons for a couple of months now and it has been invaluable. Learning a lot of theory is not really necessary, but a basic understanding can surely uncomplicate things a little. I'm almost ready to start playing a little bit of lead which is where I really want to get in order to become a more well rounded player.
I still consider myself a beginner compared to our other band members, but here are a few of my learnings. Make sure you are tuned with the rest of the band first; probably standard tuning. Learn enough theory to understand the key of a song and chord progressions. Many times the key is the chord the song starts with, but it's usually the ending chord. And, of course, there are always exceptions. Music is all about math; it's not a mystery. And definitely learn how to use a capo to your benefit. It can be a non professional's best friend for some of the tougher keys using a lot of sharps or flats.
Don't be afraid to make mistakes and don't beat yourself up too much. That's how you best learn. My teacher says there are only two kinds of mistakes - hitting the right note or chord at the wrong time or hitting the wrong note or chord at the right time. The point being that timing is the most important. You can't afford to stop and correct your mistake because the rest of the band is going to keep moving and keeping time. There are only 11 major notes or chords and you're not likely to make 10 mistakes before you land on the right one.
Sorry about the rambling.....enjoy
David