The first way to increase your Bitcoin is by "Buying" as much as you can at current price and hold them later sell for profit.(Risk Involved)
Second way is to offer service for Bitcoins and "Earn" more Bitcoins and increase your BTC holdings.
Third way is to "Invest" in Altcoins and hope that their value will increase in future and sell them for Bitcoins.(Risk Involved)
Fourth way is making few Bitcoins off "Giveaways" check out games and rounds board.

Good Luck! Hope my post helps you.