Earning bitcoins can be done on all kind of methods but I think one of the best is signature campaigns due to the fact its easy and profitable.
You got almost no risks and its safe to do all the time.
Though signature campaigns are the most risk free and easy method of earning money through bitcoin but still we should always keep in mind that it is not a permanent source of income for us as the campaign we are in can anytime stop it and then we will have no place to go if we were just relying on it, so it is always better to have multiple ways of earning bitcoins.