Nikon d5000 How to get crisp pictures?

I have a nikon d5000. I'm in the learning process of photography. I shoot natural light only. I can take clear/focused pictures fine but its the color that I can't figure out. My whites look grayish not bright? I see other pics and they are really crisp white and I can't figure out what to do. Any suggestions?

If you aren't shooting in manual mode the camera is probably underexposing the image. The camera can't tell the different between bright and white, so it tries to make white into a gray color which is incorrect. You need to add some exposure compensation to your photos if you are noticing thing.

Natural light can be a pain as you're finding out - especially indoors - there never seems to be enough of it.

Either add light or use flash. If you compensate that may help some. If you raise you're ISO you
risk noise above 800. I did a couple of shots indoors yesterday, with flash, but still I needed to run my ISO to 400 and all went well - no noise at that ISO level.

Your exposure could be wrong (under exposed). Solution: shoot in manual mode or learn to use exposure compensation. Exposure compensation is disabled in Auto mode. Use Program, shutter, or aperture modes to use exposure compensation. Be sure your camera is set to matrix metering. If you shoot tricky shots where there's lots of variation in bright and dark areas, auto exposure will probably do something bad, so you might want to consider spot metering. Your lighting of the subject could also be an issue.

White balance. Auto white balance usually works fine, however, it is better to manually select your white balance to match the conditions you're shooting in. If your white balance is off, you will end up with a weird color tinge on your shots. For critical shots, you can shoot a gray card so you can adjust white balance in post processing.