The following is a list of things that you can do to help boost readership of your stories (aside from just writing it well and having a good summary, which is a given). I compiled it from general observations I've made about the most popular fanfics I've read, personal experience, and from marketing techniques that I've learned irl.
☆ Talk about it in other stories
Mention, very briefly, in your relatively short author's notes (the ones at the bottom of chapters, not the top), the other story you're working on (to create some interest/excitement). When done in a tactful way, this can compel people to check out your other story(ies) (it's worked on me before!). You can do this before you start posting a new story (to drum up anticipation) or while you are posting a concurrent story. Include a one-line summary of what readers can expect from the other story.
☆ Draw fanart
Draw fanart for the story before and during the posting of the story (beyond just the cover art). If you really, really can't draw, get someone else to do this. The better the fanart, the more interest you'll spark towards your story. Make sure the fanart has a link to your story (or edit the description and add a link once the story is finally posted). Only post one link - the less options, the easier it is for a person to decide to read it... i.e. send them to ff.net, ao3, gaia, or wherever, but ONLY to one of them, not to all of them. The fanart, however, can be posted in multiple places, and will probably garner more attention to your story the more places it is posted. Unlike the next tip (youtube video), I've seen this make a significant difference in the amount of response a fanfic gets.
☆ Youtube video
Not as necessary, but a youtube video that promotes your fanfic in some way is an added bonus.
☆ Social media
Be social; people love to chat, so get involved in your fan's community and every once in a while mention the fanfic you're working on (if the situation is appropriate to mention it), or at least, include a link to it in your signature. Basically, make some friends - people are more likely to read stories from their friends than from people they don't know at all.
There's probably even more that you can do in this regard, but I haven't actually looked into this method too deeply (not yet anyway… I intend to do more research here for my own personal interest sometime in the near future). I have seen someone post sneak previews to the next chapter (while they're still working on it) on tumblr. Their fanfic is one of the top followed/faved/reviewed in its category on ff.net (it's in the top 15 stories in each of those fields out of 17,000).
☆ Respond to reviews
Respond to reviews for all your stories; people love to be acknowledged. And when you acknowledge them, they will start to like you. They're more likely to read a new story posted by someone they like or feel a connection with than from someone completely new and whose stories they've never read before. Plus, it encourages them to review more often.
☆ Update CONSISTENTLY
This is probably one of the most important things you can do. Update on a consistent schedule, whether it's once a day, once a week, or once a month, BE CONSISTENT and always update on time. Let your readers know when you will be updating/what the update schedule is (every Tuesday, or every second Saturday, or on the 15th of every month, etc). If you aren't a consistent writer, then do not post anything until you've completed the story (it'll be easy to update on a consistent schedule when everything is already done).
Marketing is all about getting a product in front of a consumer, on a CONSISTENT basis, because consumers will forget (out of sight, out of mind). By showing up at the top of the page on a regular basis, you will gently remind readers about your story, get them in a rhythm of anticipation and relief (that builds as long as the consistency is there… a long hiatus between updates totally kills this), and it can attract new readers too.
When in doubt, think about it this way: if you updated everyday for five days and then didn't post a new chapter for six months, your readers won't remember or care that you had been consistent at the beginning and it'll take a lot to get them back into your story... as opposed to updating once a month and by the sixth month they're ready and waiting with excitement for the next chapter, knowing it's about to come out right on schedule.
Is it really okay to update it only once a month? Yes (though it may also depend a bit on fandom). That story that I mentioned above that's top 15 out of 17,000 is updated once a month. There are a lot of people who love to read manga that comes out only once a month, and some of those are seriously popular series (D.Gray-man moved to a monthly schedule before going on hiatus and was still very popular, Fullmetal Alchemist was always published in a monthly magazine, and despite it's supposed bi-monthly schedule, Skip Beat!, more often than not, comes out only once a month). The more often you update, the more readership you will garner, so if you can keep up the CONSISTENCY, once a week or even more often than that is still a preferable option.
☆ Get people talking about your story
Referrals are powerful. Amazon.com's business is heavily based on this concept for good reason. People are more likely to take the word of some unrelated 3rd-party reviewer than the word of the company themselves about how good a product is. The same goes for fanfics. I can't tell you the number of times I've seen someone mention in an author's note a fanfic by someone else that they really enjoyed and in some way inspired their story, which compelled me to go and find that other story and read it too.
I've seen fanart drawn by people who were inspired by a story (and, since they were inspired enough to draw it, they also raved about the story with the highest of praise and gave a link back to it). I've seen authors mention their beta's works (with brief summary) as a recommendation. Heck, I've even seen some community forums built around the discussion of a specific fanfic (which brings everyone together and gets them talking about that story). People talking about your story will bring more readership to your story.
If you're struggling with this point, then maybe one of the following could help (I haven't tested it with fanfiction, but it works in almost any real life situation).
---> Politely ask people who like your story to mention it to their friends who may be interested in reading it. ("Hey, if you really enjoy reading my story, please recommend it to your friends. It would mean a lot to me. Thank you!")
---> Exchange influence; recommend other people's stories in your author's notes/social media/etc. And, if the person you're recommending is someone who also reviews your story, you could politely ask for them to do the same favor in return. Being someone else's beta-reader might also fit in here. Oh, and review other people's stories. A lot! I've got a couple of very faithful reviewers for my stories. Whenever I see their names, I automatically feel connected to them (all warm and fuzzy and liked by them!). And because of that, I've read and reviewed their stories too.
---> Create a space in which you are an expert (for example, a forum thread discussing a point about the canon of a series that you've heavily researched beyond what canon has given… like digging into medical conditions or something related to the canon, expanding on a theory). After getting a good discussion going, share a link to your story and briefly tell people what it's about.
---> Create a referral system whereby you reward people who refer your story to others. I'm not entirely sure how this would work in the fanfic world… but perhaps you could offer to draw fanart or write a short fanfic (even 100 words) as a challenge for anyone who recommends you to their friends. Not sure how you'd track that though… nor how much work you'd end up having to do. Hmm, you could also maybe send them the new chapter ahead of posting it for everyone else to read, but irl the best reward for referrals is money -- something that your clients aren't already getting from you -- instead of more of the product or a discount on the product that they are already buying from you. In any case, this is certainly a guerilla tactic that you can be creative with if you can find a way to get it to work for you.
---> Exchange influence; recommend other people's stories in your author's notes/social media/etc. And, if the person you're recommending is someone who also reviews your story, you could politely ask for them to do the same favor in return. Being someone else's beta-reader might also fit in here. Oh, and review other people's stories. A lot! I've got a couple of very faithful reviewers for my stories. Whenever I see their names, I automatically feel connected to them (all warm and fuzzy and liked by them!). And because of that, I've read and reviewed their stories too.
---> Create a space in which you are an expert (for example, a forum thread discussing a point about the canon of a series that you've heavily researched beyond what canon has given… like digging into medical conditions or something related to the canon, expanding on a theory). After getting a good discussion going, share a link to your story and briefly tell people what it's about.
---> Create a referral system whereby you reward people who refer your story to others. I'm not entirely sure how this would work in the fanfic world… but perhaps you could offer to draw fanart or write a short fanfic (even 100 words) as a challenge for anyone who recommends you to their friends. Not sure how you'd track that though… nor how much work you'd end up having to do. Hmm, you could also maybe send them the new chapter ahead of posting it for everyone else to read, but irl the best reward for referrals is money -- something that your clients aren't already getting from you -- instead of more of the product or a discount on the product that they are already buying from you. In any case, this is certainly a guerilla tactic that you can be creative with if you can find a way to get it to work for you.
☆ And… that's all I've got!
Have fun writing your fanfics and go out there and boost your readership for them!
