There are a few things that can make your biscuits not as fluffy as you would like. I have listed them here: 1) Not using enough baking powder or baking soda. 2) Using old baking powder. You should replace baking powder every 3 months. 3) Too much liquid. Some of the dry ingredients may not be mixed well enough into your dough, causing a wet dough that will result in a dense biscuit. To fix this, make sure you mix all the dry ingredients well before adding any liquids. 4) The oven temperature is too low, which will cause your biscuit to take forever to rise. 5) The oven temperature is too high; this could burn the outside of the biscuit before it has finished cooking in the center. Try lowering your oven by 25 degrees next time you bake and see if that helps. 6) The oven is too hot, which can cause your biscuits to rise then fall when they are in the oven. This will give you very little flakiness and an overbaked exterior. Lowering your oven temperature by 25 degrees should help with this problem as well