You didn't state your target audience. The following, in random order, could be important.
Shooting mode: auto, program, aperture priority, shutter priority, manual, and idiot modes.
Focal length.
Exposure metering - matrix, spot, center weighted.
Continuous mode shooting and why you might want to leave it in continuous mode normally.
Diffraction (why you shouldn't use a really tiny aperture).
Filters for lenses (polarizing, UV, gradient, tint).
Diopter adjustment for the eyepiece.
Formatting the memory card.
Recovering accidentally deleted images.
Image stabilization.
Slowest hand-held shutter speed one can use.
Image quality versus ISO setting.
Sensor size (APS-C and full).
Lens distortion.
Timer mode.
Rewind for SLRs and how to load/remove film.
Exposure compensation.
Lighting.
Fill flash.
Tripod mount.
Light meter (older SLR issue).
How changing f-stop relates to shutter speed regarding exposure.
White balance.
Film types (Velvia, Ektachrome, Kodachrome, Pan-X...).
Pixels and how many pixels do you really need.
Image compression (JPEG high, low, med; raw and the various forms of compression used in raw).
DPI (why you shouldn't think DPI unless you're printing)
Downloading images to a computer.
Image manipulation programs.