Keeping track of bar inventory especially beer and liquor.

I receive and sell liquor and beer on a cash basis, when receiving the inventory from the vendors what is the best way to input and keep track of the inventory? IE we by the beer by the case but we sell individually by bottles or in 3 or 6 packs. when receiving the case as inventory do you than input 24 each vs 1 case? Also for the liquor we purchase the bottle and get about 25 - 30 shots from a 750ML bottle do you input 1 when receiving the bottle or do you input 25 meaning you will get 25 "shots" when that bottle is empty? Any help with this is greatly appreciated.