Article: of liquid per every 1 cup (236 ml) of flour called for in the recipe.  Reduce leavening agents by about 1/8 tsp. each time you make the recipe until you end up with an ideal flavor.

What is a summary?
Use more liquid by adding 1 tbsp. Decrease the amount of sugar by as much as 1/4 of the total amount used in the recipe, since sugar causes flour to become dry. Decrease the baking soda or baking powder if you notice a bitter flavor the first time you attempt a high altitude quick bread recipe.