I would say the best method to grow your Bitcoin would be using your BTC to start a gambling site, since 50% of Bitcoins economy is gambling...it would definitely profit you.
I didn't know that. If that is true then it's amazing.
But I wouldn't say that starting a gambling site would definitely profit you though. We all know that it depends on many factors, it's not so easy to definitely have profit at something.
This is much easier said than done. You need skill for this or to pay someone to do it instead of you. Then you still need skill running these kinds of sites.
Also, there are many gambling sites out there at the moment. So you would need to work hard just to prove yourself and gain some market share. All in all you need a lot of money just to start something like that.