What are your main referral sources?

I'm having an issue with https://indiebrands.io/ - Almost 40 - 50% of our traffic is from Twitter. I was able to reduce it a bit with some SEO work & building our own audience through a Newsletter.

But I still have the opinion that this is way too much. So I'm interested to hear what you'll have to say. What are your main referral sources? How did you build great referrals & generate traffic? And most importantly; how did you know what could make for a great source?