well, if you write Exo..that's already one step inside the exposure zone although there might be a lot of competitions since it's one of the popular tags here....honestly i have no answers since...i don't. my own fics have almost no readers n it's not like i write anything popular anyway so that's expected. i think...updating frequently will help, showing consistency..the more you update, the more the fic will appear on front page of latest updates n more chances to be seen. i remember writing a fic...with absolutely no reader/comments of unpopular group/ship...but after like five-six chapters updated...i started getting some readers...n it feels satisfying since i didn't try to cater to the readers' taste here but they just got interested on their own accord...i also have seen a fic, very well written, of a popular fandom/drama...but no comment at all n just a few subs...but the writer keep updating...and after about 20 chapters...she started getting some ardent fans. i guess it depends on luck n your popularity too. being an active reader to other writers' fics can help too. some writers would find interest to check out your fics when you constantly give feedback to theirs. other than that, advertise is the fast way. when all else fails, money works. haa. good luck~

i suppose you could always write about popular ships or popular plots. i'd recommend really making sure there's no glaring or consistent grammar mistakes, as those can be serious turn-offs for prospective readers. i'd also tell you to avoid cliche plots, but some people might enjoy that, so that's up to you to decide. aside from that, you can always advertise on people's walls (if they haven't indicated that they don't want ads) or find an advertising shop to do it for you.
even if you just choose to write a story and not do active promotion, you'll still get readers :) it'll be slower that way, though