Check out this Food Network recipe from Alton Brown's Good Eats (or clip on YouTube). Brown is very good at explaining how, what and why. If your biscuits are too heavy and crumbly, it means you're working the dough too much, breaking down the fats. Check this discussion at Chowhound: The less you handle the dough with your hot, sweaty hands, the better. Use a food processor to pulse the butter/lard (or refrigerated or frozen bacon grease, mmm mmm) into the dry ingredients until you get a very coarsely-mixed meal, then pulse in the liquid until you have a very sticky ball of dough.

Hands off is also the secret to amazing pie crust. Really, do yourself a favor and watch Alton Brown clips on YouTube. He can be quite geeky, but the man knows how to teach both the history and the science behind, well, good eats.