It took me about a month for my novel to break 25 subscribers. I promo daily on Facebook & Twitter, and I check these forums daily while trying to reply to at least one thread. Any comments I get on my novel I do my best to reply to them or at the very least heart them. I update my story every Friday, and it seems to help if you can maintain at least one episode scheduled so people know you're series is alive and well! 
But I really don't know what really works because I've gotten over 30 views on the most random in between days.
I didn't have any base to start with other than the two friends that kept encouraging me to publish. One of those friends started posting his story at the same time (@HippieGhost) and it took him about a month as well to get his first 25. Both of us avoid the sub for sub because inactive readers does nothing to help you, and it can actually be extremely disheartening when you update the story and get no response from them.
Edit: I also just started posting on Instagram to promote as well and I started using my Twitch to promo (had no followers on there before hand) . So It really comes down to luck and how much time you invest I think