AO3 doesn't HAVE an algorithm, and people really need to figure that out.
If you want to see something you have to search for it. Follow tags. Engage with people.
And if you want to write a story, write it, put it up, and then TALK to OTHER PEOPLE about it.
Be interested to be interesting.
Feral Kwe -- Elidibus Truther
The number of "interest posts" for fics I have seen on AO3 going "I have an idea but I'll only write it if people say they're interested" goes with this. The people who can't figure out the AO3 algorithm and complain about how to get more hits.
Write with your dick not, for profit/popularity PLEASE