There are many ways to grow your Bitcoin but i think the best way is trading and investing.
Trading is the best way to grow your bitcoin but in the first place you need to ask yourself if you are ready of doing so. There are a lot of traders now and even those new investors are taking up the risk and they are buying their own alt coins and choosing it for their own portfolio. You buy low and sell it on high prices, just repeat the steps and you'll grow your bitcoin in due time.
Trading is the answer but it's not something that everybody can do. Instead of this, you can start to learn about mining. It's a more guaranteeed way of increasing your bitcoin number.
I prefer mining because of this reasons.
It's a fact that not everyone can trade and prefer to grow their bitcoins through it. Just go with mining through your hardware and stay away from cloud mining. It's been exposed and everyone knew it already that cloud mining are risky and others are turning in to a real scam. It's guaranteed to increase the number of your bitcoin but if you prefer to mine bitcoins, I prefer to mine altcoin and then sell it to bitcoin.