There are lots of tips out there for ensuring an adequate supply of breastmilk: drinking dark beer,eating oatmeal, taking herbal concoctions. Sure, these may help, but there is one thing that is the most important to ensure an adequate supply of breastmilk:
Allow the baby unrestricted access to the breast. The more the baby nurses, the more milk the mother will produce.
Supplemental feeding with formula, especially during the first 3 months of breastfeeding, can inadvertently sabotage a mother's milk supply. Additionally, bottle-feeding with pumped breastmilk can reduce the mother's milk supply. Why?
Mother and baby have been perfectly designed to make breastfeeding work. The more the baby stimulates the breasts, the more milk the mother makes. The more the baby is given something other than breastmilk, the less the baby is stimulating the mother's breasts, so the less milk that is produced.
Use of pacifiers can also result in a reduced supply of breastmilk. Pumping breastmilk does NOT stimulate the breasts the same way that a nursing baby does, so pumping rather than nursing can also reduce milk supply.
I experienced this myself with my firstborn since I was still working outside the home. I pumped breastmilk for about 15 months so that my daughter would be able to drink breastmilk while I was at work, but it was very obvious to me early-on that I was not able to pump very much. If my daughter was nursing, the milk would just keep coming as long as she nursed (as evidenced by repeated let-down sensations and her vigorous swallowing). But with pumping, I was only ever able to get a small amount of milk at a time.
What does unrestricted access to the breast look like?