When you mean you want it to be a better picture, you have to define what is better. Whenever possible, shoot and save RAW with Adobe RGB as your profile. This is to get as much color as you can to your original photo. Process your RAW image and export the final output with the sRGB profile for printing (in a photolab/printer that requires sRGB profile) and for web display.
If you want it to pop and stand out, improve a little contrast to boost some of saturation. Check the levels of the image and expose to the right of the histogram. Default camera settings are conservative not to blown highlights but will give you dull white and dull colors. Sharpen last your processed photo for web display or every time you downsize them to final output for printing. This is not about the camera, it's about digital image handling for better output.
When you want your photo to really catch the attention of the viewer, start with a nice composition by directing the eye of the viewer to your intended center of interest. Expose the scene right the first time you record it to avoid lesser to no exposure adjustments during post processing. A scene that is exposed well will give you better details. With a D90, you can preview your depth of field before taking the shot, use it and adjust your aperture accordingly. Take control of your camera and not the other way around. It is this way you can maximize its use for better output.

Keep up the good work and keep shooting.
