If you are in desperate need for available light, set your iso on 200 - 400, and leave it alone.

Adjust shutter more than any other setting. WATCH YOUR LIGHT METER (usually some sort of bar system on the display/viewfinder) then adjust your shutter to balance.

Run aperture from 4.0 - 7.1 for run of the mill picture taking. Run higher than 7.1 if you reallly want a lot of depth, i.e., landscape shots. Run lower then 4.0 when you a) really need light b) really want shallow depth of field. Everyday shots: f/5.0 - 6.3