Anything but gambling I guess!

You can earn money with money then convert money to
BTC 
I think gambling is not the best way to earn money because gambling its not good. You must claim faucet or joined a signature campaign to earn free bitcoin no need to invest just you have to do is apply a sig campaign and make a post so its very simple to earn bitcoin.
Gambling is no way to earn money, it's a way to lose it.
Of coures somebody hits a big pot every now and then, but on the long run the house will always win.
And that means the customers lose.