The most popular and trusted method to earn bitcoin is Signature campaign. Many other option is also available but i think the best other option is buy some bitcoin.. then wait for sometime till value increase and then sale them.
Trading bitcoins is actually one of the best and most profitable ways of making bitcoins if someone can afford it, but not everyone can afford to buy enough bitcoins that can generate enough profit for him over the time he will have to pass for selling them back, that is the reason why people prefer ways to earning bitcoins rather then buying them.