Your initial rough storyboards should be done small so they are quick to do and easily changed.
Your final storyboards should be done on 8.5x11 sheets of paper.
Use black/colored pens/markers. Do not use pencil because it is hard to see when scanned.
Each storyboard should have a brief comment at bottom indicating the camera angle/shot (see WT - chp 3).
Camera movement (if any) should be indicated, e.g. crane shot, pan, dolly, etc (see WT chp 3, starting on p. 46).
Movement of characters (if any) should be indicated. Keep continuity in mind (WT - chp 8)
Think about the visual elements, framing, and perspective in each (WT - chp 5 & 6)