Gather all your beauty products in one place, like a countertop or on an old sheet or towel on the floor. Compiling all your products in one place allows to you see just how much you have and where you have duplicates, making it easier to decide what stays and what goes.
Depending on just how much you own, you may want to start with your makeup, then once finished, move on to lotions and bath products, then hair products, and so on, breaking up the task into manageable sessions.