In a body milk or facial moisturizer, you're looking at about 90% water to 10% oils. In a light lotion or thicker facial moisturizer (like a night cream), you'd have about 80% water to 20% other things, like oils. In a regular lotion, you have about 70% water to 30% other things. And in a cream you'd have about 50% to 69% water and 31% to 50% other things.
When I'm making a cream, I want it thicker and more tenacious, so I tend to use stearic acid. For a lotion, body butter, body lotion, or facial moisturizer, I tend to use cetyl alcohol because I'm looking for something to glide over my skin with very little whitening. (This is just something I noticed I do...this isn't a hard and fast rule...) Body butters and creams tend to have more butters than a lotion, and facial moisturizers, light lotions, and body milks don't tend to contain heavy oils or butters.
I'm sure I'll think of more as time goes on...any other helpful hints from lotion makers?