A combination of things--Facebook ads, Twitter (not as much these days), BookBub ads, and lately I've been trying some AMS (Amazon) ads to see how they go. The BookBubs were a huge help, numbers-wise. And the old adage about your next book being the best marketing tool has worked well for me. I've got 9 out now and the next one will be released in June.
That number is just Amazon, I realized - Smashwords only goes back 360 days, and there's another 3,000 or so in that period but since my first BookBub was before that, I suspect it's more like 5,000.
I need to stop coasting, though, since I've noticed my sales are down a bit over the past couple months. I need to refresh my ads, and I'm thinking about switching to Kindle Unlimited, as I've heard that's potentially more lucrative in my genre (urban fantasy) than wide.