- ISO: Be sure the camera is at its default ISO if you have plenty of light. This speed provides the best image quality.
- Exposure compensation: This is my biggest mental challenge! I seem to always forget to zero it out and I use compensation a lot, so I end up shooting with compensation that I don't want the next day. Check it.
- File size: Check to be sure you're using the maximum (largest) file size and the best quality level. On my Nikon D90 (if I'm in the jpeg mode), for instance, this means "Fine, Large" or "F" and "L." Memory cards are almost free they're so cheap these days, so always shoot at the largest file size.
- White balance: Either set it to the type of light you're using (sunlight, etc.) or just leave it in automatic and the camera will adjust for the existing light color.
- Exposure mode: I usually keep my camera set either to program or aperture-priority to start and then move to another mode (like manual) if I need to. Don't just assume it's in the program mode, check to be sure.
- Battery level: Ideally you should have checked this the night before, but always be sure you have battery power. I own several extra batteries that (fortunately) fit all of my Nikon bodies and so I always have at least one fully charged. I've always liked cameras that also accept traditional batteries because that way if you run low you can just run into a drug store and buy a fresh set.
- Clean lens: Be sure that your lens (or lens filter) is free of major smudges or dust. I keep filters on all of my lenses so rarely have to clean a lens, but the filters are sometimes a real mess. Use a microfiber cloth to clean them.
1 hour ago