I've been playing guitar for a little bit over three years now. Sometimes I practice every day, in busier times a bit less, but I've been doing it regularly and know some stuff beyond the beginner level. But until now I've done it alone. And I am REALLY struggling to get to the point where I can play with other people. It is so frustrating. People have this "just do it" attitude and I get that it works with most. "You'll know what to do. Play a couple of notes, see if that works and just go from there" - I've seen that myself many times. It seems so easy. However, this feels not at all comfortable to me. But I also know that I can't spend the rest of my life playing music alone in my room.
Can somebody give me some advice? I am searching for something in between the "just do it"-attitude and burying myself in music theory books - both doesn't seem to work for me. Is there something specific that I can prepare for? Like a checklist? This is not about practicing cover songs with anybody. I want to improvise a bit with other people. And add some useful stuff to a jam session.
EDIT: Wow, thanks for all your answers! I didn't really know what to expect here, because I think it's a difficult question if one of the issues is something as vague as "not being comfortable". That was exactly what I was looking for.
EDIT 2: I really liked the idea of having a setlist as a part of preparation. The statement "This is not about practicing cover songs with anybody. I want to improvise a bit with other people." was badly phrased. Want I meant was that the jam session I have in mind is not so stiff, opposed to everyone having his music sheet and playing exactly what he practiced at home note for note. But what and how exactly I want to play is not that important here