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 not even a sort of work or a job. it is just a game which depends 100% on peoples luck.
I don't consider gambling as earning. I think better to do small and various freelancer jobs to earn bitcoin. or just stay with your own job.