how to product more breast milk

When my sister had her first and second child she has a difficult time producing a milk. As much as possible she really wants to do breastfeeding to all her child cause as we all know that breastfeeding is one of the important things a mother can and should do, not only for her child, but also for herself. Sissy was very frustrated knowing that she don't have enough milk to give to her child. She did a lot of tricks to be able to do breast feed even though she's hurting. Now, if you are a new mother and you happens to have the same problem like my sister read and learn some information on how to product more breast milk in that way you will know what to do.