I just self-pubbed a few days ago so I don't know either, but...
I self-published a collection of 100 flash stories, but nearly all were previously published in litmags and anthologies. That exposure probably provides a boost once people find out my book exists.
I'm sure it depends, too, on how popular the genre you write is. For example, erotic romance or SFF novels tend to have a higher following than books of short stories.
Also, "lazy" things you can do might be the most effective. The first day, I only sold two ebooks even though I was only charging $2.99. And I knew both of my buyers, lol. The second day, I signed up for a Kindle promotion that makes the ebook free for 5 days. On just the first day of it, I "sold" nearly 200 copies.
In theory, some of those readers will leave reviews, which boosts future sales. And there's word of mouth, which also boosts future sales. But it's too soon to tell how much effect it will have. Plenty of people probably nab anything free but never read it. But we can only do what we can do...
The first day it was free, it reached #1,200-something in free Amazon ebook sales, and #10 in free ebooks of stories by a single author. The increased visibility further gets my book and name out there.
Another easy-peasy thing is join Goodreads and put a few forthcoming print copies (they don't take ebooks) into their "Giveaway" drawings. So far nearly 200 people have signed up for a winning copy and it's only a couple of days into the month I signed on for. Again, more visibility and readers, though where that leads remains to be seen.
Also, list it here. This is a big site, it will get some notice. I mentioned mine on Twitter and a few other sites I'm on as well. But of course you can't blab about it too much or it comes across as spam and just annoys people.
I also listed it on my author site.
So there are a few lazy ways to get some attention on your book. But during the first day, when I did just slap it up there without doing a thing, it was lost in the masses and didn't get noticed at all.