How much oil should I use on my face?

It depends on each oil type, as each is intended for a slightly different purpose. 

A good guide line is to apply a few drop to a cotton ball, (if you are applying the oil directly to your face) and dab the cotton ball onto your face and then gently massage into your skin. 

If your skin feels too oily then that's a good indicator to know that you've used too much and you can refine for your next round. 

If you find that you can't massage enough into your skin and feel like your pulling your skin around then you've most likely not used enough of the oil.