One of the ways and the best way is to Buy BTC at cheap rates then when the prices go up
Sell them
That's it
This way you can keep earning
Yes this is a good way to increase bitcoin but you really need to be a day trader and you need to allocate a lot of time when you will do this type of increasing bitcoins. Because there are times that the selling rate is low and you don't have choice to wait for it to become higher upon selling. This really requires patience and also calm mind.
Not everyone that we prefer to become a trader is match with trading. A part of them fail on their trade. But remains of them can success with keep learn and experienced. So other ways to earn bitcoin as step to increase your bitcoin (balance) is do a job that you can receive payment in bitcoin.
Yes having a job that will be paid with bitcoin is also a good way to increase your bitcoins. As long you can find a decent one and that is going to hire you continuously, because there are some companies that are going to pay you within their contract and doesn't have any plans on keep on continuing. Investing your profit from that job is also good.