The short answer is you don't. Writing is a long game. You start off way behind and overwhelmed, and many writers give up well before the finish line. The very first thing you have to ask yourself if you really want to be a professional author is "Do you really love to write?" Well do you? Punk?
You're training to fight Chuck Norris and his roundhouse kick and all you have is your pet turtle to train you. He's not even teenaged or mutant or ninja. If you don't love the fight and can't stick through the training then now is the perfect time to give up. I know that sounds like shitty advice, but if you're not in it for the love of the game then get out. If you can't stick to it until you do climb that mountain of success using mighty Odin's beard then the best advice I've heard is to not waste your time.
People point to the overnight successes in the industry. They are the exception not the rule. There are many reasons for their success but talent and hard work are first and foremost. Sometimes being in the right place at the right time gives them that extra push to reach the top of their mountain a bit quicker. Many of those author's "overnight" spans 10+ years, but no one sees that through their rose colored glasses.
So what does work? How do you promote and gain a larger following? How do you win at this game where you are an author writing stuff and then a dump truck of money pulls up to your lawn? I don't have those answers. I am just like anyone else howling into the void of the twitterverse trying to get a food pellet and hoping that one day I will be one of the success stories.
The best promotion is word of mouth from someone else. The best way to get that is to put out a quality story then another and another. Keep writing until the bones in your fingers poke through your skin, and then wrap them up in bandages so you can continue to write. It all revolves around hard work. This is part of the reason why I haven't been blogging as much. I'm trying to get my first novel out, then my second, and so on.
Social media isn't the best way to get the word out, it's the best way to interact with your friends and fans. That is how people who enjoy your work will find you. If you're Mr or Mrs. Spammy Spamerton then they are probably going to tire of you. Social media is all about individual interaction. People want to see your face on there, not your ass. So hit me up sometime. All my social media accounts are linked to my smartphone.