Seaford Folk Club books a guest almost every week we are open so that's about 40 a year.
Members ask for performers they have seen and liked.
I sus out good performers when I go to festivals or other clubs. Sometimes I hear a really good CD and am tempted but a CD does not tell me that the performer can 'work' an audience.
Quite a few people get bookings if they come along and do a floor spot and go down well.
I book up to 18 months in advance but usually have some vacant slots that can be filled at short notice (3 months).
The festival I co-organise does not book guests but some cracking performers have turned up and got local bookings because they went down a storm there.
Hope this helps
Mary