What's worked well for me is to shoot in "P" mode, and lower the ISO to 400 or so. Let the camera pick the shutter speed and aperture. Then look at the results, as well as what settings the camera used. If you're happy with the results on the LCD, shoot away. If I'm "close enough", I may switch to Av or Tv, still with fixed ISO, and adjust aperature or shutter speed to get what I want.
Most often, however, it's go to manual and starting with what the camera picked in the first shot, increase/decrease shutter speed to brighten/dim the picture (or highlights), and increase/decrease the aperture (f-stop) to reduce/enlarge the depth of field (area in focus). Of course, changing the aperture will require corresponding changes in the shutter speed and/or ISO to get the same exposure level.
Recognize that some shots, such as a clear night in Los Angeles (very rare) shot from high in the hills, require shots in the 30 seconds and longer to get it 'just right'. Depending on your camera, there may be "long exposure noise handling" capabilities which, if enabled, may take a minute or so to 'process' the picture before you can take another shot.
At a minimum, you'll need a tripod. Ideally, you'll be using a remote release and mirror lockup to completely eliminate all camera shake.