Need advice for my Nikon D3100 - how do I take better pictures?

So I just got my Nikon back in August, so I'm still kinda new to this thing and I want to learn how to take better pictures. Anyway, I feel a little lost now, and I think some constructive critic would help. Tips and ideas would be great.
Here are some of my best photos so far: http://ditteharring.blogspot.com/2011/09/this-is-art-or-not.html
Please tell me, what you think I could do better.
And I'm going to a big city very soon, and I'm going to bring my camera with me. Any advice for that?

These are beginner's snapshots, with no real photographic merit. If they are what you want, fine, but in the greater scheme of things they are of no general interest whatsoever.

If you really want to improve your photography, you should read books or look at tutorials on photographic basics: exposure, lighting, composition. Take a class. Join a club.