There are two ways to earn free coins or tokens and they are Airdrop or Bounty campaigns. But from the both of them, i think the bounty campaign is best.
For it first of all you will have to achieve Jr. Member rank on this forum. Then find a best and suitable bounty campaign from Bounty section for you.
Here you find different options for earning in bounty like Twitter, Facebook Signature Reddit, Translation etc., and now decide which campaign you want to do.
But according to me signature campaign is the best campaign because it is highly paid-able section of all other options of bounty and it also increase your knowledge about crypto currencies. So now decision is your's.
Yep i agree with bounty is best, but in my opinion try to focus on high paying bounty activities, for example translation or bounty managing, this can bring you a lot.