If you mean doing a real job or giving effort. The freelance jobs are the best source of bitcoin. They pay you in bitcoin.
I know they pay with bitcoin but only for those who are qualified to do the job, if your skills are on demand then you can get a good salary.
However, I am done with that kind of payment system as you cannot maximize your earning since you only have a limited time, I know some people does not consider trading as a job but it is for me now, I can consider it since it gives me steady income and I am happy as a trader, maybe that is my secret.