How can I keep my milk supply up?

Breastfeed and pump. If a baby is not breastfeeding often enough, or is not drinking enough milk from the breasts at each feeding, then the mom can use a breast pump to maintain or increase her milk supply. She can pump her breasts in between breastfeedings and/or pump right after each breastfeeding. The milk can be stored in a freezer for later use.
Empty your supply. Keep yourself well nourished, well hydrated and rested (as much as you can!). Actively empty your breasts with feedings or pumping to allow for maintenance and increasing of your supply.