One of the first things I've noticed with my camera is how much lighting changes even by just turning around. For example, when I was at my
bro's police academy graduation, I had my settings adjusted for the stage lighting, where my brother would be walking across the stage. But then the speaker asked the parents to stand up. So I saw an
opportunity when my ma and pa stood up next to me on my right, I just went ahead and started clicking away. But as you can tell, the lighting was not the same. So, all that to say: I need to learn how to adjust my settings quicker and when to do so.
And a practical tip I've learned the hard way; set your ISO higher before slowing down shutter speed or changing anything else when taking indoor pictures. I've found indoor lighting is almost always darker than you think it is.
UPDATE: 1/7/09
Here, the only difference between these is that the second picture is one f-stop higher. It should have been lower to begin with, but it works for illustration purposes. You can see, that there is almost no detail in the face of the one dog in the second picture, but if I felt like cropping the first one a bit, you could actually see the dog's face a bit more. This is how much difference there is in lighting, just by turning around.
I hope this helps