Anything other than signature campaigns and gambling.
A bit saved is a bit earned. So save your money by not clicking on any of the signatures of the people posting in this thread.
just common advise

anyway gambling is just worth of luck and its up to the user how he/she will use her bitcoins. Still be wise on using it.
I think many who suggest trading, I think because currently only trading with the US could produce bitcoin faster than mining or signature campaign.
Trading is more risky and you can't always win with your trades. It can be equated to calculated gambling in the sense that you must have some knowledge in trading and not just depend on pure luck. Also, there are indicators that serve as guide although they don't always result in yields. For me, I just stick to signature campaign and make a little something on my free time.