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.
I was surely not talking about HYIPs and Ponzis. My indications were towards the opportunities out there where one can increase his bitcoins. One such example is Bankroll Investment. Investing bitcoins in gambling bankroll can make you shared owner of the respective gambling site and you can make good returns in bitcoin.