I use big chain ring in front for flats and down hills and sometimes even slight rolling hills. Remember that the changes with the chainrings in front will be big changes. The gears in the rear simply "fine tune" it. There is no right or wrong. I will say that I used to always coast downhill and sometimes get a little "wobbly" going too fast, so now I shift to a high gear (big chain ring front & smaller cog in back), and pedal downhill and I have more control of the bike and it's not wobbly! Seemed counter-intuitive at first, but it's true.