The general rule on cadence is that when your pedaling rate slows down (below 90rpm), shift down, instead of grinding. (Of course you shift up when your feet feel like spinning off the pedals, but everyone knows that!) The exception to this rule is on a climb. You’ve shifted down a few gears, been climbing for at least a minute, and have reached a steady state. Now you are approaching the top and can see the crown of the hill. You might be a little toasted from the extra effort, and slowing down, cadence falling to the 80s like a bad new wave band. So, time to shift to an easier gear, right?
No! It is time to shift to a harder gear. Huh? If you go easy, your speed will drop just as the road is getting less steep. You will be passed and probably wobble a bit. Instead, shift up to anticipate the flattening road, push a little harder, and get your cadence up to the 90s. Your perceived effort will remain the same and you will accelerate, zipping past that newbie rider. Now you are ready for the descent as your speed is rising. You can always recover on the downhill.
So, when you almost at the top of your next climb, shift up, give a little kick, and show that hill who is the boss! Your friends will be amazed as you pop forward. Great job!