AW: mehr kontrast
The image won't ever be mint sharp with a cheap kit lens, however almost any lens has a sharpest aperture. Just set your camera to aperture priority and shoot something with fine detail using the same viewport but different apertures. I recommend the lables of beverage cans. Place one dead center, another one at the margin of your image (as lenses are sharper in the middle, clarity is falling off with increasing radius). Use a tripod, mirror lock-up and everything fancy you can think of to reduce camera shake. Compare results, check which aperture is the sharpest.
Also make sure your shutter is fast enough or you'll encounter motion blur. Don't be afraid to increase your ISO some stops. I don't know the D40's sensor, just test noise levels yourself.
Contrast isn't up to your decision, it's mostly a camera/lens property. A polarizer can improve contrast by a huge amount, but it's not an option for snapshots, as it requires some time to adjust it to the right angle. For your purposes I guess it's easiest to just play around in the RAW converter.
