I'm in the same boat as you. The advice I'm going with so far is go with more volume in one space instead of going wide with Twitter, youtube, etc.

So focus on posting and engaging (and getting more engagement) on one platform at a time before expanding.

I recently asked this same question in my local tech community, and largely the response I got was that a lot of freelance developers, especially if solo, will mostly get work through their professional network. That's been the case for me and others I know.

So on top of social media/content marketing, are you building your network as well? Start locally in your region and expand outwards.