If you have a typical "trigger shifter", you can push 2 or 3 gears (kind of depends on hand/finger size & ergonomics) with one thumb stroke & repeat.... Just keep turning the cranks with lighter force. It kind of becomes necessary if you suddenly have the traffic light change while you're cruising in the higher gears and want to avoid being stopped in too high a gear.
(I just drop my triple to the granny ring and push a couple times with the thumb while braking on my 3x9's)
You can "release" the other trigger repeatedly quite quickly and pretty much do the same thing to move to the higher gears/smaller cogs.
Just practice a bit and you'll get the idea.
Find an isolated parking lot/road and just work on it a bit.
It'll become 2nd nature.