The Rules of Pumping:
1. You can't look at the pump. Stress effects your let-down reflex (let's call it a milk ejection reflex-- who wants to be let down???). If you are looking at the pump and thinking "there's nothing coming out!" then your body says stress and your breasts don't work as well. (I found that shopping online for jewelry helped me relax when I was pumping. Other people read magazines, look at pictures of their kids...see the page on going back to work...)
2. You can't assume that what you get pumping is what the baby gets when you nurse. No breastpump mimics a baby's suck and it's really hard to bond with a pump. Both factors combine to make your expressed milk less than what your baby can get. So, if you are pumping 4 ounces, your baby gets at least 4 ounces when they eat at the breast.
3. You cannot assume that your baby has been starved all along when they slam the bottle of expressed milk. Babies respond to a hard nipple with milk coming out and that's what a bottle nipple is. The catch is that they cannot control the rate of flow like they can when they are nursing at the breast, so they eat very fast, whether they want to or not. This inability to regulate the flow of milk from a bottle leads to kids eating lots of air and was the reason that we started burping our babies. Breastfed kids fed at the breast usually don't need to be burped.
4. You should be pumping as often as you can. Every three hours is optimal, but sometimes not do-able. Plus, clock watching causes stress, and stress is no good for anybody. Your pumping session should be for what feels like 10 minutes and can be interrupted. It doesn't have to be 10 minutes, or 10 minutes straight. You can pump for what feels like 5 minutes, answer the phone, go to the bathroom, and pick up a little later and finish that pumping session.
5. You should pump one ounce for every hour since you last fed or pumped, and that's a two-breast total. So if it's been 3 hours since you last pumped, then your next pumping should yield 3 ounces total.