Your biscuit ingredients really matter. Here are three areas that I find are most important when making biscuits.
1. Baking Powder
One of the most important parts of a fluffy biscuit is the baking powder. Make sure your baking powder has not expired. If it is "dead" your biscuits will not rise. Instead, they will be flat and hard.
HOW TO TEST BAKING POWDER
Add ½ cup of hot water to 1 teaspoon of baking powder. Does it bubble? Then your baking powder is still active. If there is no reaction, your baking powder is useless. Throw it away.
2. The Fat
Originally biscuits were made with lard, or rendered pig fat. That is still a great way to make fluffy, flaky biscuits. Another healthy alternative is to use real butter. (Contrary to much nutritional advice, natural animal fats are not bad for you.)
3. The Milk
Use whole milk or buttermilk for the best results with homemade biscuits. Buttermilk not only adds a wonderful flavor to your biscuits, it also adds a delicate texture. If you don't normally keep buttermilk on hand, a great alternative is buttermilk powder. Mix it with the amount of water called for in your recipe. I normally mix it with milk for even more flavor and tenderness.
However, you can simply add the buttermilk powder in with your dry ingredients and proceed with the recipe as normal.