Anyone have advice for a Nikon D5000?

I bought this camera more than a year ago but i feel like i still haven't used it to it's full capabilities. I'm still learning how to use it in dark light and too bright light, and i feel like there's something i don't understand. When i want to take a night landscape or anything in low lighting how can i adjust the settings to achieve the most stable, focused photo?
does anyone have an opinion on the lens that originally comes with this camera? If there are problems is it due to the body or the lens?
and if you have experience with this camera i would be grateful for some tips, somethings i should look out for or things i should take advantage of.

Deep blue has given you a perfect answer

For night photography (or any long exposures for that matter) you need a tripod. I would recommend you keep the ISO fairly low (100-200) and if you are taking cityscapes at night, you generally want a deep depth of field, so aim for an aperture of f11-f16.
Your shutter speed will then be whatever the light meter determines it needs. If it's over 30secs, you will need a remote release to lock the shutter open in 'bulb' mode.

If you can, use a remote release in any case to trigger the shutter (less camera shake), but if not, then use the self timer to trip the shutter.

The 18-55mm kit lens is fine - although if you want to improve picture quality, user skill and lens choice are far more important than the camera body.

Are you shooting on Auto modes? Or have you ventured into manual or using +/- EV comp to override what the camera thinks? Remember, YOU are the photographer who makes the creative decision as to where to 'place' your exposure - don't be ruled by the camera!

There are some good books about on using the camera manually - Bryan Petersons 'Understanding Exposure' is a good one. Also, think about joining a local camera club - you'll get a lot of help & feedback there & it's often useful to be able to talk to someone face to face.

Your problem may be that your using an auto mode like aperture, shutter or program auto mode. In all these modes the camera uses its internal meter and looks out and judges how bright the scene is. This works good in a lot of normal everyday situations, but if you are trying to shoot a bright scene like snow or a dark scene like night, those modes will fail you and you must use the manual mode.

Here is what happens: Your cameras meter judges how bright the scene is, and tries to adjust the settings so that nothing is too dark or too bright. This is called middle gray. When your shooting at night, the camera tries to adjust things so that the night is now middle gray, what a failure. It gets bad in show too, the camera sees how bright it is and tries to make it dark, now snow is gray and not white.

Here is how to solve that issue, get ready to take a picture as usual at night and put it on manual mode. What you want to do is close down the aperture or increase the shutter, or perhaps both from what your used to. This is probably going to be somewhere around three full stops.take a shot and then look at the histogram, the peaks of the histogram should be more on the left side, probably a lot more. Keep adjusting until you get it right. Now if you want to shoot snow, you do the opposite, you open up the aperture and make the shutter open for a longer time. The histogram for snowy scenes has most of its peaks on the right side. Either way, the secret is to take it off any auto mode.

If you're having problems getting the camera to focus during night scenes, use a flashlight to light whatever you need and the camera should be able to focus.

Your cameras meter judges how bright the scene is, and tries to adjust the settings so that nothing is too dark or too bright. This is called middle gray. When your shooting at night, the camera tries to adjust things so that the night is now middle gray, what a failure. It gets bad in show too, the camera sees how bright it is and tries to make it dark, now snow is gray and not white.