The best way to reestablish mild supply is to express more milk more often. Your body will create the supply it thinks is being used, if you have milk left over after breastfeeding, your body will produce less, if you breastfeed until there is none left, your body will produce more.
To reestablish your milk supply, there are many things that you can do. You can take herbal medication that will increase your milk supply, but the easiest way is to pump. Pumping will give the body the idea that milk is needed and it will start to produce. Be sure to pump both breasts equally.
The more frequently you nurse, the more milk you should make. However, if you are doing this and your baby isn't gaining weight properly, you'll need to supplement with formula.