No gambling or risky methods
just guaranteed methods ?
just invest you bitcoin in trading, we can say that there are big money in trading. if we only know how to use it to choose what coin do we need to invest Im sure that we will be having a very good amount of bitcoins. But I prefer you should try that pure mining I said everyday you will earn no investments needed, sure income in a very easy way.
Trading is too risky and OP is looking for guaranteed methods. I would say there isn't guaranteed methods, but there are other investments safer than trading which you just should try if you have experince with this kind of activity as you can lose the $80 very fast... Mining is hard also and unprofitable in many cases as he needs expensive ASIC machines to start mining and need to have access to cheap electricity to make it worth, maybe mining altcoins can be a good deal, but too risky also for who wants guaranteed methods.