First, a disclaimer: I am no publishing/marketing expert. If you want to get a really savvy opinion on how to sell books and gain followers, you'll probably have to look elsewhere. But if you want to know my personal strategy, it would be, "One at a time".
Books are written one word at a time.
Followers are gained one person at a time.
Sales are made one book at a time.
In other words, there is no fast dash to succeess, but rather, compunded progress over a long stretch of diligent work.
Granted, some books come out and become instant bestsellers. One can sit around and wait for this big discovery to happen. If people just go crazy over a certain book, its author doesn't really have to worry very much about a platform. But these cases are few and far between. This is why I consider it a worthwhile investment of time and planning for me to build a platform.
This means consistent presence online on my blog and social media, engaging with people on a personal basis, and collecting emails for my mailing list, which consists of fellow authors, bloggers who have previously reviewed my books, and readers who have contacted me out of interest in my writing.
And, of course, in between all that, I mustn't forget what makes me a writer in the first place, which is, naturally, writing. This is something I like to tell to every overwhelmed indie. If all your marketing and networking activities leave you no time to actually write, it's time to reevaluate your priorities. The more you write, the better you become at writing, and the more books you have out, the easier it is for people to find you.
Being an author means constantly chipping away at stones made of writer's block, rejection letters, a tough market, and various disappointments along the way. Patience wins; each day may seem like the one before, but when I look at what I have accomplished, I am reasonably satisfied. I currently have six fiction novels out, with more coming soon; I have a publishing contract, some sales, some good reviews, and some people who know my writing - considerably more than a year ago. I will keep moving forward to the next steps and climb them. One at a time.