I think doing freelance online work is a good source of bitcoin. So I am honing my skills so I freelance very well.
if you have skills on the computer why not joining at freelance works. doing photoshop and some other works will let you earn bitcoin from it. using your skills from earning is one way to earn bitcoin. but if you dont have skills in computer lets say that you are on the other field of work. better try gambling or trading in bitcoin.
Gambling is not a good source of bitcoin. It is very difficult to make money in gambling because beating the house is almost impossible. You will just lose more than what you earn in gambling. Trading is a good source of earning bitcoin. But is not that easy to do. You must know some strategies to it like reading the graphs or knowing when to buy or sell at a right time.