One of the things that you are going to have to do when you decide to self-publish is use social media. Get over your fear of Facebook and Twitter and learn how to use them. Those are the ones that I use the most and I have done some actual experiments where I did not post my links to my various books to Twitter and found that sales have gone down.
You will hear a lot of people talk about all of the other areas and things you need to do. You'll hear about email lists and sending out monthly email newsletters. You will hear about using Facebook ads, GoodReads, Pinterest and all kinds of other stuff. For me, the best areas have always been Facebook, Twitter and a blog. I recommend that you get those to start with.
Why not an email newsletter? Look, I personally hate going to websites that always want you to sign up for their newsletter. I have an email inbox clogged enough already, and I don't want more crap coming to me. I know, I know, you have a built in audience in which to market your latest work, but the thing is you have to give something away to get people to sign up. It has to be something that people want, too, so be prepared to write a story or several stories, or create a boxed set, and then give electronic versions away to everyone who signs up. Plus, I am not entirely convinced that if Amazon finds out, they could reduce the number of reviews allowed or even ding your books. I hear that this doesn't happen - but I swear that Amazon. Is. Everywhere.
Facebook is the one I use a lot. I use it for personal use, but then a couple of friends created an author page for me and then turned the keys over to me. I use that exclusively for my books. I also post interesting things that I find related to writing. I promote my blog articles, journalism articles, blog tour posts and stuff about my books. I use it to promote pre-orders and books that are already on sale. Plus, using Facebook ads is easy, affordable, adaptable and great to get the word out.
Now comes Twitter. I signed up for Twitter ages ago and there was a brief window where I used it like I did Facebook. I networked with people and met some online-exclusive friends there. Eventually we all moved over to Facebook and now Twitter is almost exclusively promotional in nature. I have also hooked up my Facebook Fan Page with my Twitter account so if I post something fun, it filters over.
To manage these things, I recommend an aggregator like HootSuite HootSuite allows you to hook up Facebook and Twitter (among others) and schedule posts throughout the week or even throughout the entire month. I use their auto-scheduler so that will pick what it thinks is the best time for a tweet to publish. For Twitter, you need to post at least three times a day and one of those should be mid-day, since most Twitter followers check their feeds sometime around or just after lunch.
I always set up a week's worth of posts on Twitter using HootSuite. I am going to suggest you find an online class to learn about hashtags and things like that, but the important thing is to get posts out there. Include an image and also include a link to where someone can buy your books.
The auto-scheduler on HootSuite will plan out four posts a day. Stick with that.
Look, I use Pinterest, too. I have attempted to use Instagram - but I just don't get that one. I have this blog, use Facebook, use Facebook ads and Twitter. I have also tried GoodReads and attempted to use LinkedIn, but none of those have worked as well as the blog, Twitter and Facebook. If you find that an email newsletter then, great, but I personally do not recommend it.
So, there you go. My tips for you young writers out there. Good luck!