Don't go higher than iso 3200, try to stay at 1600/below. Use a flat picture profile, use a fast lens(2.8 minimum pretty much, 1.8/1.4 would be better, although at those apertures you'll need it to be using a wide lens or the dof will be too shallow to film with)
If you haven't read the user manual, do that right now. The answer is simple: you use whatever settings will give you enough light. This is all going to depend on how much light is there, what kind of image you want (fast vs slow shutter speed), etc. We can't just tell you what the "best settings" are. Do some research
As a general rule you shouldn't go over 1600/3200, but sometimes to get a useable shot you need to go up to 6400. Yes there will be a ton of noise, but its better that than recording 3200 and it being too dark to use. A faster lens (like a canon 50mm 1.8) can get much better shots at low light without having such high iso. I'd recommend getting that lens as a starter lens since its only $100 and is extremely useful.
"you know when you see a edit with there colors boosted and they really hd?" -coleaddison
"When there are more people in your organization who believe Obama is a Muslim than believe in the theory of evolution, there is a problem." -colbert
Don't you ever go up to ISO 6400 like someone said above. There is no "ideal" setting for every dark scene. Depending on what you're shooting you may need different shutter speeds and different apertures. A tripod makes it a million times easier to shoot stationary subjects as you can drop the shutter speed right down and then you're free to choose aperture and ISO however you like. If you're shooting moving subjects then you will need a faster shutter speed so you don't blur your subject. Practice practice practice. Practicing in different scenarios is the only way you'll truly learn, it's really not that hard to figure out on your own through trial and error