Your shampoo is only there to clean the roots and surrounding area of your scalp, along with the top portion of your hair. Its purpose is to clean the oils and greasiness from your locks, and this should only really be on the top of your head. So, a dime-sized amount of shampoo will be enough to cover your needs. If your hair is particularly thick, you may need to wash it once, then rinse, and repeat. For conditioner, you need to use just enough to coat the entirety of the bottom two-thirds of your hair. This doesn’t need to be a thick coating, just as long as there’s enough to provide some nourishment.