The simplest way to increase your bitcoin is investing them in projects which pay a higher interest rates or you can indulge yourself in trading in the market with your funds.The other way is you earn by working in different ways like joining campaigns or writing blogs over internet and get paid in btc or work in company that pays you salary in the form of Bitcoin.There are several ways and it is you who has decide the best suitable way to increase your money with your knowledge and skills.
I wouldn't recommend someone to invest in any project that promises to pay "a higher interest rates". Time and again hundreds of such projects have came and went, scamming people out of their money. You must have a clear understanding of how the project functions or else one would fall into the trap of HYIP or Pozi's.
Trading is risky as well because one cannot surely predict which turn the market is going to take next.
Freelancing for bitcoin or other cryptocurrencies is the best and risk-free way to earn. Just with some initial investment in improving one's skills, you can get involved in providing your services to the world.