I would argue that there's no "best and fastest method." You really have to find what works for you in regards to tools and posting. I use Post Planner to automate my posts, but I also have to make sure that I'm engaging with my audience. You can use FB ads or Amazon ads to promote content and spread the word. It all really comes down to your audience, however, and if they are your true fans who will help you spread your content, etc. Consistency is KEY with content promotion, but also be strategic and generous so you're still giving value to people and not just spamming them.