Advice for a photography beginner?

I'm starting to pursue photography as a serious hobby (and hopefully along the line a career), so basically my question is for the more experienced photographers. My question; What do you wish people would have told you when you first started? Any general advice? I just want to be prepared.
The equipment i'm working with is a Nikon D90; lens 18-105. I'll be getting more soon, but I'm not too educated in the whole mm thing yet, and I've just learned what aperture means.

Added (1). Okay, I meant that I'm just beginning in DSLR. I've read many guides and such, but I'm just looking for some direct advice.

Start with using a phone.
n8 with 12 mp is a good choice!

To become a better photographer:

Take lots of pictures, take pictures everyday, take pictures everywhere, photograph everything, always have a camera with you. Print your pictures and review them side by side, don't be afraid to experiment, show only your best work to others (and buy a big garbage can for the rest).

I wasted a lot of time and money chasing the "perfect" camera, lens, etc when I was younger (and still do to be honest) but its far better when starting out to work with a minimum kit and concentrate on the intangibles, you need to train your eye before you should think of buying more stuff. Walk around with a viewfinder (simple piece of cardboard with a hole in it) and practice composition, walk around with camera in hand and only bring the camera up after you have composed the shot in your mind (or use your composition aid.

Learn how to use the camera properly…

http://photo.tutsplus.com/articles/round-ups/100-helpful-photography-tutorials-for-beginners-and-professionals/

Nice question…

Hmm… Get to grips with the shutter speed/aperture/iso triangle as soon as possible. Learn how your camera's meter works.
Pay attention to your post processing skills but never stop try to get the exposure as right as possible in the camera. Processing can make your pics stand out just that extra bit.

Be critical of your work, find a club, a website, anything where you can get constructive criticism instead of compliments.

Honestly? There's nothing that I would have hoped somebody had told me when I first became interested. Photography is a solitary activity: it's just you, your camera, and the subject. This is true even if you're in the midst of a score of fellow photographers. You take pictures. You scratch your head wondering why they didn't come out the way you'd hoped. You read up on it. You try something different the next time. A useful practice is to show your best work to more experienced photographers and ask them for an honest critique. Be prepared to be shocked by all the technical and artistic flaws that they point out in your masterpiece. Then you get your camera and go out and do it again.