We live at approximately 7,000 feet above sea level, so high altitude is what we do. General rules for adjusting regular recipes to high altitude:
Cookies: decrease the baking powder and/or baking soda by half and decrease the sugar a bit.
Quick Breads: such as muffins and coffeecakes reduce the baking powder and/or soda by one forth (one teaspoon becomes 3/4 teaspoon).
Pancakes and Waffles: decrease baking powder/and or soda by one forth. (one teaspoon becomes 3/4 teaspoon).
Biscuits and Scones: no changes needed.
For candy making at 7,000 ft elevation: decrease the temperature called for by 14 degrees Fahrenheit. (-14)