A very good way to earn some btc is to join signature campaign. Also you can start trading but you must be very careful if you do not have any experience.Whatever you do, avoid these bitcoin doubling sites you will lose your money in these scams.
Yeah, avoid those sites that promises high returns and almost too good to be true. Almost all of them are ponzi and scams. They are very easy to spot because they always promises impossible to achieve interest rates. If you want to invest your hard earn bitcoins, go those investment that are trustworthy.