Marketing is mostly good writing. Start by writing and opining on things you're building, or what you find interesting in the ecosystem you operate in. The more you write, the more articulate you get. Social media platforms like twitter and Linkedin are great places to start voicing some of these writings. Another way to do this is to analyse a company; understand its P&L, its business model, its growth levers and write about it obsessively. It's what folks like Packy do with their newsletters. Eventually, you get better at content dissemination; this is the second part of the puzzle. If attention spans are bad, how do you bait a reader in. How do you frame headlines and get people to read something by invoking their curiosity etc...

If you have these two elements baked in, the next step is to focus on digital and performance marketing aspects — you will learn these in 2-3 weeks tops given how simple and easy to digest they are.