Decide on the visual style of your film. Use storyboards if your film is heavy on effects or relies on non-verbal and visual storytelling, but don't if you allow extensive improvisation and flexibility to your actors. Revisit films created in a style similar to yours and examine their use of shot selection and editing.
Make a basic shot list comprised of brief descriptions rather than developed sketches. Choose your close-ups, medium shots and long shots, and from which general directions. Have an idea of the visual progression of a scene before beginning a detailed storyboard, and make this list while on the actual scene location.
Sketch your storyboard. Storyboards are not comic books. Visual and character detail is unimportant. Shading is only useful as a guide to light and shadow for your cinematographer. Cinema is a medium of movement and your storyboards should convey movements required of the camera and of your actors within the frame.
Edit your storyboard. Each additional set-up can add hours to production time. Artistically, the fewer shots you have, the more impact each remaining shot will have. Alternatively, you may find the sequence not entirely comprehensible and a new shot may be necessary to visually complete the scene.