The beginners session at Shrewsbury Folk Festival is brilliant and more festivals should have similar.

I have been teaching myself fiddle, so playing at Shrewsbury was my first time playing in front of anyone (I hadn't even played for family or friends!) It was a relaxed pace, the sheet music was available in advance, and although we were encouraged to play from memory no one was judged for using the sheet music.
I don't think I would have the confidence to join a session, without having taken these babysteps first, and it has spurred me on to keep practicing and learning new songs and has given me a taste of sharing and playing with others, which is what folk music is about.