When the combustion efficiency is improved, the fire emits less harmful smoke. The combustion efficiency can be improved with the following. Make sure that there is a sufficient airflow through the fire. When the cookstove is insulated around the fire it burns hotter and produces less smoke. Using a double wand, with air in between, can isolate the combustion chamber.
Around the combustion chamber no heavy and cold materials should be used, as these will absorb a lot of the heat. A small insulated chimney above the fire increases draft and provides a place where smoke, air and fire can combine, which decreases emission of harmful smoke.
Only the burning wood should be heated. When non burning wood is heated it will only produce a lot of smoke. (Design principles for wood burning cookstoves)