It can be tricky, but let your camera work for you. A wide aperture (lower number) will let plenty of light in, but give a shallow depth of field, a slow shutter speed will also let lots of light in, but will blur movement. A high ISO will make the sensor more sensitive to light, but also increases noise.
A tripod, or any sturdy rest will help you take non blurred pictures at slow shutter speed, Ideally, run as low ISO as you can get away with, as fast shutter speed as you can get away with and aperture as appropriate for your pictures.
I find shooting in manual gives me the most control of this, but really you need a fiddle and work out how to get the best from your camera and find its limits!
Also....... Flash, well, it has a place, as obviously it provides bright light as the shutter opens, but this is no good if what you are photographing is a fair way away. It can also bleach out shots a little. For people, you want to avoid straight on flash (in my opinion) as it can make them look very white (and bleach out highlights so they are totally white on, say, the forehead). Likewise, an off body flash below can make big shadows and make people look weird, likewise from above. you just have to experiment I'm afraid! Good luck!