This really depends a lot on the subjects that you intend on photographing: Use a tripod at all times.
If the subjects are stationary use the auto mode if there is ambient light or use flash. Keep in mind that ambient light can often create subtle effects which are often very pleasing and flash can overpower the scene producing a "washed out" effect. Depending on the available ambient light, your manual setting should last anywhere from 15 seconds up to 2 or 4 minutes.
If your subjects are moving, then use a flash, set your camera shutter setting to 60 (the traditional shutter speed when using flash). For people, have them look at your shoulders or just below the camera to avoid the "red eye" effect.
For special subjects such as fireworks, lighting strikes: set the camera on a sturdy tripod, aim in the general direction of the action, manually set the shutter speed to "B" (bulb). The shutter will remain open so long as you depress the shutter. You can obtain multiple images on one frame with this method.
Consider using a remote trigger or cable to minimize camera shake.
There are many more tips but these are the basics.