Everyone says Gary Vee but truthfully you need to find multiple sources.
Personally I stopped looking at social media as an answer and more like a targeted bullhorn for my content.
I'd recommend you start with here.
If you're looking for a book, I really like Epic Content Marketing.
For general guides to Digital Marketing, I highly recommend Neil Patel's Quicksprout. Just read everything he has there, especially his Guides in the right sidebar. Extremely thorough, very well-researched, and lots of references to other sources.
Good luck!