it's not a secret actually ,If you browse the forum regularly you can surely find some ways to earn Bitcoin.Your earning amount depends on your skills,If you have some skills like trading, programming, development etc then you will be able to earn more than 0.1 BTC per week.Again, Without investment you can earn up to 0.1 BTC per week by joining a signature campaign.
Even earning from signature campaign needs some knowledge about something like mining, economy, trading etc. However earning from signature campaign is much less than the other options as trading or offering skills, totally depends on the ability, skills and knowledge of the user. A good designer or developer earns far more than the usual content related freelancer (on an average) so make sure that we are giving priorities to the right things & options.