How to make extra crispy and crunchy breading like KFC?
First, use self-rising flour or use 1 teaspoon of baking powder added to each cup of all-purpose flour that you're using for the dredging and coating mixture.  The carbon dioxide produced during frying will cause the coating to expand and become more flaky.

If you want more tender and flavorful chicken, first brine the pieces in buttermilk that has been mixed with several tablespoons of salt, some black pepper and whatever other seasonings you like.  Otherwise just dip the chiken in buttermilk seasoned with salt and pepper. 

Before dredging the chicken, sprinkle a little milk or water over your seasoned flour mixture.   Shake the flour mixture around so that it asborbs the liquid, this will help create small crunch bits that will later adhere when you dredge the chicken.  Dredge the chicken and then return to the milk and then dredge again to get a thicker coating of flour.  Deep fry in enough oil to submerge, or pan-fry in enough oil to come about 2/3 up the chicken and turn a couple times to promote even browning.  Alternatively, after pan frying until evenly brown all around, remove from oil and place on a baking rack on a sheet pan and finish cooking in the oven until the chicken is done.