Should I Use Flash or Increase ISO?

It really depends on what you are taking a picture of. Sometimes it is not possible to use your built-in camera flash in a low-light environment. For example, if your subject is standing far away, you might not be able to reach the subject with your flash. In that case, the only solution is to either come closer to the subject, or turn off flash completely and use a higher ISO. Obviously, for landscape or architectural photography, you should always turn off your flash, because it will not be able to brighten up the entire scene. So in a low-light situation, the only two options are to either increase the ISO so that you can shoot hand-held, or set the camera to the lowest ISO and use a tripod.