Why did we put this last? Even if we believe that you don't necessarily need it for success, advertising can help you scale. However, take note that you can waste a fortune on ads without seeing many results if everything else is not in place in your online business.
You can expand your reach and generate high revenue and brand awareness through pay-per-click advertising or PPC and social paid advertising. It would help if you used Google AdWords and Google Analytics simultaneously to do PPC well. You can pay Facebook, LinkedIn, Twitter, YouTube, etc., to have your content shared through "boosting" or designing unique advertisements.
You will come across most of the abovementioned skills, develop, and learn them as you build anything online.