There are many ways to increase your milk supply. The most important thing to remember is breastfeeding works with the principle of supply and demand. The more milk output is demanded, the more your body will supply. In other words, the more you breastfeed or pump ("emptying" the breasts) the more milk you will make. However, the idea that you are ever "empty" can be confusing because your breasts are never truly "empty" of milk when you are nursing. Your milk is made up of live cells and is constantly being produced… similar to how the body makes and replenishes its blood supply.
If you need to increase your milk supply, try increasing the frequency of emptying your breasts either by increasing breastfeeding or pumping after feeding the baby or in between feeding sessions. This will encourage your body to make more milk while still having milk to satisfy your baby during feedings. However, if you are concerned about your milk supply or are having difficulties with milk supply contact an International Board Certified Lactation Consultant (IBCLC) in your area.