Have had the pleasure of playing in a band for many years with Kate Barfield who to my ears is a great master(mistress?) of this art. She uses the under-the-chin hold, fairly loose when she is singing. She tends to play a chordal rhythmic(shuffle or whatever) accompaniment,and fills in gaps between lines melodically a lot ofthe time, as a blues guitarist would. On slower things she often plays the tune along with her singing, with drone notes filling out the sound.