Free methods:
1. Faucet (do referrals, don't go clicking faucets all day)
2. Solving captchas (pretty good rates if you surf this forum)
3. Paid-to-click (paid in Paypal though)
4. Signature ad Campaign.
Investment Methods1. Investment site (of course)
2. Gambling (risky but if you've got a good strategy or if you're pretty good at it then do it)
3. Trading (needs knowledge)
4. Making your own faucet sites/rotator
5. Exchanging currency (BTC >> Paypal, PM, Skrill, etc)
6. Buy a higher rank account here and join signature campaign (You should know the rules first in this forum)
7. Buy a mining hardware (don't do cloud mining it's not profitable anymore)
Those are the methods I know. I hope this helps. For me, investing in a bitcoin casino is the best investment right now.
There are tons of methods out there to earn bitcoin. All of them requires basic knowledge, so better research about bitcoin more. And also if you're gonna choose a method, try to research how it works first before you do it.
Cheers!