In my opinion the best methodes to earn bitcoins online are the signature campaign, trading, and selling your skills/services or goods online for btc. You can use them or just focus with one if you haven't the time or the needed knowledge about the other ways.
Signature campaigns are a proven source of bitcoins with a minimum skills needed unlike trading which needs skill and a good eye for price movement.
you also earn bitcoin in gambling, but if you try the gambling make sure that you are ready for the consequence of this.
Gambling is a high risk game and i honestly think this should be for people who dont mind spending/lossing
Also, you can use lending of bitcoin but before you lend your bitcoin make sure for the collateral and be sure that you lend to the trusted people to less the risk you want to take.
Depending on which platform you choose to lend out your btc this should be a slow way to grow your btc and maybe low risk in some instances