Drink lot of soup, especailly papaya and fish. It did increase my supply. I find drinking water is not as effective as drinking soup.
There're foods to avoid too: any kind of liver, foi gras, pate, black bean(chinese preserved one), wheat gem.
Also seeing a lactation consultant is helpful too. I hads a lot(really a lot) of blocked ducts and the milk just couldn't come out. She may give you useful tips to increase the supply.
Happy Breast Feeding.