If you are approaching a hill (before the hill or just as it starts), shift the cogs to a higher gear and then shift down to the granny gear. Then you won't feel like your pedals are spinning. It also helps you feel like you have more gears to shift down to on the cogs as the hill gets steeper. Do not wait to do any of this until you are going up the hill or you will drop your chain... or not be able to shift at all.