My first rule, don't be affraid to practice, practice teaches you more than anyone speaking to you and saying do this or that. It imbeds to your brain better if you attempt a shot, fail, make corrections and then become successful. More so than someone telling you to do something for a shot.
Do not shy away from night photography. Some of the most breath taking shots can be had with back grounds of cities, bridges and neon lighting in dark settings. Dusk and sunrise can be so incredible and no two are ever alike. Always use a tripod for night/low light photography with no flash. Stay away from high iso settings for the night shots, this will net you digital noise, sometimes overwhelming in the picture.
The two key manufacturers for DSLR's are Canon and Nikon. Neither of them make a bad camera. The low end models in their lineups have more features than may will ever use. I personally am using the heck out of my Rebel XTI and I have had a few other bodies, but I like this one the best. More so than my shortly owned 40D and my used 5D. I have become a Canon fanatic now and it's my prefered manufacturer.
If your able to afford a good DSLR, do not skimp on lenses. Many people short change the lens. A sub par camera with high end glass, will crush a high end body with a low end lens.
Be aware of dust particles landing on your equipment, below I have a sample sunrise shot overlooking Lake Michigan from Chicago. The wind was up a bit and dust unknowling landed on my equipment. Falls back on what Dark said, be aware of your surroundings.
A couple recent shots messing around with my XTI: