As already said bitcoin is already a good investment, but i believe the op wanna to invest the btc into others ways to get more bitcoins, casino bankrolls and few altcoins might be a good investment, outside those you will have to start your project, but be sure competition is very strong at the moment.
In that case one should just speculate BTC against fiat (or a pegged asset as Bitissuer's). Sell BTC when high, buy when low.
Disclaimer: we are Bitissuer devs.