Buy goods that people need / want and sell them for Bitcoin, you can turn a small investment into a profitable amount of BTC in no time.
The main issue in goods trading is you have many rivals and you must try hardly to get trust from people, so they would prefer you instead of others. And, when you do your business, there will appears new rivals with same products time by time.
Well I think, the best possible way to Grow your BTC is through online gambling. Be a good sports analyst and you can double your earnings in one click. If you are really good at analysing sports. Then there will be a huge possibility to double or triple your bitcoin in a day.
Its a wise way to people who like to use strategy in gambling. If they dont want use any strategy, then they could go to dice site. But dice site is not recommended to grow our bitcoin.