Trading is the only way to grow your bicoins in short term and apart from that I don't find any concrete way to grow bitcoins as you can never depend on gambling to grow your bitcoins as you will be surely loosing everything in it.
yes trading is a good way of making money but in fact trading require a lot of experience and for getting experience you need to spend much more time in trading, and only then you can become a good trader and can make more money from there. in very beginning you need to start from small amount so that if you are losing money you should not be effected so much and can easily bare the lost.