1.) Size the combustion chamber for the required task
Whatever fuel is loaded into the stove will be burned at a rate proportional to the amount of air made available to it. In most cases, more fuel loaded means more firepower because there is always excess air. The fuel is exposed to the air above it! When cooking small amounts of food, when not much power is required, load a small amount of fuel into the stove, or use a stove with a small combustion chamber. For cooking lots of food at once, use a stove with a big combustion chamber.
2.) Charcoal stoves can have high turn down ratios
The primary air supply to a charcoal fire can be reduced close to zero and the fuel will keep burning. Once the air supply is increased, the firepower will increase. Normally there is a spike in pollutants when the air supply is increased sharply, but it will stabilize once the firepower comes back up.
3.) Use high heat and jets of secondary air to burn up the Carbon Monoxide
Insulate the stove body to get higher temperatures in the combustion chamber and to loose less heat into the body of the stove.
4.) Put the pot close to the charcoal
This will maximize heat transfer from radiation.
5.) Use a pot skirt with small channel gaps between the pot and stove. 8mm usually works well.
This will maximize convective heat transfer.
6.) Maintain constant cross section area throughout the stove
This will help to keep the velocity of the draft high assisting heat transfer efficiency.
See “Clean Burning Biomass Cook Stoves” for further details and a CAD drawing of a modern charcoal stove.