Ah, fear of jams is one of the few topics on this forum at which I am an authority. I went to my first jam a little over two years ago, so the experience is still fresh in my mind. I used the verneq method and didn’t play my first time. I didn’t even take any instruments so I couldn’t be talked into playing. I just listened and met a few nice people.
When I went back a few weeks later with my guitar, my heart was about to beat out of my chest and I probably would have hyperventilated if it hadn’t been for a couple of shots of liquid courage. Most of my anxiety was caused by the thought of singing in front of other people -something I had no experience doing. I worked up two or three songs that I figured I could make it through (not sure if I actually did because I’ve crashed and burned so many times since then I can’t keep track) and stuck to the script.
I continued on like this for probably the first six months -forcing myself to go despite my anxiety. Over this time I learned some things, though, and they were things I never could have learned picking in the sterile environment of my living room.
The first thing I learned was to not take myself so seriously. I was way more concerned with my flaws as a musician than anyone else was. So, I learned to laugh at the stupid things I did instead of freezing up.
I also learned how to play songs I didn’t know, just by watching and listening to other people. I remember being amazed at how fast some of the folks could pick up on a new song, but over time it seemed less amazing and more natural. If you are not a guitar player you should learn how to recognize guitar chords being played by someone else. And learn how to play simple banjo rolls over those chords. You’ll wind up doing this way more than you will play the fancy breaks that you’ve worked out ahead of time. I find that when I play dobro at a jam, people appreciate even the simplest of breaks, which for me is usually just playing banjo rolls over chords. As time goes by, you’ll figure out which songs are most common at your particular jam and be able to work out more complex variations.
Another valuable piece of knowledge I picked up on was how to select songs to play at jams. If I work out some awesome song with a complicated progression that sounds best if I sing in Eb, it’s probably going to fall flat at the jam no matter how good it sounds at home. On the other hand, an old standard with a simple three chord progression in a favored key (like G) usually works great, so much the better if it’s a sing along. I’m always searching Youtube for such songs and I save the more complicated songs or odd key songs for smaller sessions with friends.
Over time, I’ve learned how to play with pickers of varying skills. I’ve figured out how to sneak in quietly with very talented people who I can barely keep up with, and how to gloss over the rhythmic mistakes of new pickers. In short, I’ve learned how to be flexible, and enjoy making music no matter what might be going on.
I guess the point of this rambling post is that you can’t really prepare yourself completely for a jam. Like Mike said, you just have to jump in and do it. And you’ll probably embarrass yourself a few times in the process of figuring everything out. That’s just the way it goes, but you’ll wind up being a more complete musician (and you’ll have a lot more fun, too).
I’m two years into jamming once or twice a week consistently and I still get a little jittery before a jam, especially if it’s not my usual jam, but now I’d call the feeling excitement rather than anxiety.
So, jump in and get started. Once you do, you’ll probably wish you’d started sooner.