Learn your open strings and the first four frets on each one. Know what those notes are, and know where they are.
From there have your friend tell you what chord progression the song is, or what chords you are going to jam. If he can't do this, you are trying to play with an idiot and it's flat not going to work, sad but true. Assuming your friend is not an idiot watch his hands so that you know what those chords look like and you can change with him.
Next have him play a bit of it for you so that you can learn the strum pattern/rhythm of the song. Without it you are lost.
Finally simply play the roots in time with his changes, DO NOT IMPROVISE UNTIL YOU CAN DO THIS WITHOUT THINKING ABOUT IT. As you become comfortable with the changes and the timing you can start to ad little flourishes.
That's as basic as jamming can possibly be.
From there have your friend tell you what chord progression the song is, or what chords you are going to jam. If he can't do this, you are trying to play with an idiot and it's flat not going to work, sad but true. Assuming your friend is not an idiot watch his hands so that you know what those chords look like and you can change with him.
Next have him play a bit of it for you so that you can learn the strum pattern/rhythm of the song. Without it you are lost.
Finally simply play the roots in time with his changes, DO NOT IMPROVISE UNTIL YOU CAN DO THIS WITHOUT THINKING ABOUT IT. As you become comfortable with the changes and the timing you can start to ad little flourishes.
That's as basic as jamming can possibly be.
