Expressing milk is a learned skill. It is common not to get much milk at first because your body has to be conditioned to "let-down" your milk in response to the pumping. When your baby breastfeeds, let-down (or milk ejection) happens automatically, and most mothers have three or four of these let-downs during a feeding. The baby's suck, the warmth and softness of your baby's body against yours, and your loving feelings cause a hormone to be released that causes the muscles around your milk-producing glands to squeeze and milk ducts to dilate. This literally pushes your milk out of the breast. If the let-down doesn't occur, the milk stays in your breast. The trick to effective pumping is to learn to let-down to the pump. Practice is the key. In the meantime, you can pump one breast while the baby breastfeeds on the other, which triggers the let-down in both breasts.