I am a Nikon owner as well. You can find some of my photographs in the "what's your real passion" thread in off topic.
First of all you should learn to post process your photographs on a computer (color balance, levels, curves etc.). Buy Photoshop Elements or download Gimp for that.
Also, do you already know how does shutter speed, aperture and ISO setting affect the pictures? That knowledge is not essential to be able to take photographs with a DSLR camera, but it never hurts to grasp some theoretical fundamentals
Here's a good beginner's tutorial I found...
http://lifehacker.com/5815742/basics-of-photography-the-complete-guide