Burton:
Another thing to ad when going to a jam:
Find someone that is just as serious as you are about playing and on about the same level and play with them from time to time. I jam from time to time but nothing is better than picking another day to meet up with 1 or 2 of the others and play the same song maybe 10 times in a row for each to work out their part/break. If more than 2 or 3 are there then it quickly turns into a jam, instead call this “practice” and limit it to 2-3 people, 2-3 people that do not mind playing rhythm for you 10 times or so in a row to help you hone your skills on your part, then likewise do the same for them.
Almost all of us were weak-knee’d and scared the first time or so, it passes with time.
Also learn the theory part of the major scale, this will tell you 90% of the time the chords that you could use at any given time. So for instance if someone says we are majoring in the Key of “G” then if you know the chords of the major scale then those are your options…in “G” they are: G, Amin, Bmin, C, D, Emin, and F# dim. The F# diminished rarely ever shows up except for a version of the D7 and I’d say that 80-90% of the players can’t even make an F#dim chord if asked to, so forget about that chord. So now you only have a few options of chords that you are going to. Most of the time it will be a 1-4-5 type progression with a turn-around using the same 3 chords. The “1” is the G, the “4” is the C, and the “5th” is the D.
There are exceptions to these rules, but for most standard tunes this will more than likely hold true.
In “western civilization” music there are some pretty cool rules that hold true 90% of the time, learn a bit about them in “theory” and in practice and it should help you a lot.
Good luck, I enjoy trying to help others as I was very limited in my resources growing up/when I started learning, most of it was by ear and repetition in years of playing, I then decided to attempt to learn scales and theory and then and only then did it all actually start making sense.
EDITED:::::Had my chords mixed up on the 1-3-5…should have been 1-4-5