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.
Good thing there is this forum and we are exposed to not just sign up with those doubling sites. We know that there have been a lot of that lately so we need to stay careful with that one.
To be honest there is nothing like doubling your coins and if there would be something like that then everyone would be millionaire, the only way to double your coins is to double your efforts.