Earning bitcoin without investment is such an easy thing to do. Signature campaign is definitely the best way to do it. There are faucets, paid to clicks, micro tasks, etc. but those don't pay that much at all. It might pay a lot but only when you have thousands of active referrals. But that's not going to happen to most of us. Signature campaign is still the best.
You can also participate to bounty campaigns like twitter and facebook campaigns. After you have made enough money, you can try out trading. Trading is the next step towards making a lot of bitcoin. At first you will fail miserably but that's okay. Eventually you will learn how to trade right.
Indeed. This is where I started also, though I was also doing faucet way back then but I realize that I'm just wasting my time on it, that is why I'm only focusing on the Signature Campaign right now, and to the social media bounties just like what you have mentioned. Signature Campaigns that pays weekly is a good start, but Altcoin Signature Campaign is still the best one for me, the distribution of token might take some time but it is worth to wait.
And after you earned bitcoin and keep earning on bitcoin, you could start this investment by holding it on your wallet to have profits in the long run or do anything where you could get something in return.