F is one of my favorite keys to jam in. I call F the friendly key. The major scale, the dominant, and dorian scales are all real nice and ergonomic and have a nice flow on the harmonica. Also the minor pentatonic scale is my favorite in this key with an intuitive breathing pattern and the slide stays in the whole time. Because the slide is in you have an extra layer of expression by virtue of being able to do “slide bump” grace notes into the target note. Volume 1 of my new harmonica method teaches you how to get around in 4 keys; C, F, G, and D.