Find the little gear ring up front and the large gear in the rear. This is your lowest gear the bail out gear. Now practice shifting to this gear while riding on the flats. On the flats and in the lowest gear you may not be able to pedal fast enough to provide any thrust into your bike but you can take a quick look to see that you are in the gear. Now shift up until you can pedal at the speed that you like for a minute or two and then shift back to the lowest gear. Once you have this shifting memorized all you need to do is to shift to the bail out gear for the hills and then let the cadence fall where it may. In my bail out gear, I can't maintain a high cadence on the tough hills. Even in bail out gear mashing is required for some hills.