You could try trading e.g. trading Bitcoins to an altcoin, wait for the price to rise, trade the altcoin back to Bitcoin.
There is also gambling, but of course there is an element of risk.
Honestly I think the best way to obtain Bitcoins is just to get a day job and covert some of your fiat to Bitcoin. Much more efficient, and less risky, than trading/gambling.
I don't recommend this, but you could also try to scam someone