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.
But you also need a large amount of btc's to be invested as no player will play in a gambling site if the site has less bankroll.
You also need a team here includes coders, developers, support team etc. which are also part of your financial expenses regularly together with promoting, advertising, hostname etc.
There's a hidden expenses to so watch out.