The histogram is a live-graph of pixel count relative to luminescence value, or more simply, contrast and exposure. The more the graph leans to the right the more it indicates over exposure (in some elements) with the tallest spikes indicating "clipped" or burnt pixels. Or, no data. Values expressed far left indicate dark shadows. I high spike to the left indicates blacked out pixels or "crushed."
In short, the easiest way to use a histogram is to watch far right to avoid hard spikes that nuke all the data that cannot be recovered. This tool works with every ISO in the camera range.
You are correct, higher ISO will introduce more pixel noise, but this is not represented in a histogram, but rather the ISO itself. Most newer bodies will produce low noise up to 3200 ISO. Many pro-sumer bodies won't show much noise even at 6400. I squeak up to 12,800 ISO on my Canon pro bodies before noise is an issue.
With regard to shutter speed, with a non-stabilized lens, the old rule of "faster than focal" still applies. If shooting, say 70mm focal length, you just want to be faster than 1/70th of a second, which in practical terms would probably put most people at 1/125 second.
At any rate, most images that "don't turn out well" are usually more about composition, contrast, and exposure than anything else.
Fun stuff. :)
