I don't really have any concrete, number-based goals. When I notice I'm close to a certain round number of subscribers (most recently 150), I might mention that when I'm promoting. But primarily, I want people to subscribe who are actually interested in the story, which is why I haven't been as active on the promotions forum as I once was. I'm conflicted, because I do notice upticks in views and sometimes subs when I post here regularly, but I definitely notice a big uptick in people subscribing and maybe rapid-firing a few likes, then messaging me demanding I subscribe to their comics/novels and give them likes in return. I get it, it's hard out here! You want to use any means necessary to get eyes on your story. But it always leaves a nasty taste in my mouth, and I don't like having a full list of subscribers who aren't there out of any genuine interest and won't actually engage with the story beyond that first flurry of likes given in the hopes that you'll return the favor.
Now, don't get me wrong, I think there's a lot to be said for exchanges, where writers read and support each other, but that includes genuine engagement and community-building (which I wish I were better at in general). I think some people definitely manage to find that in the promotions forum (I myself have made some great friends here on Tapas!), but I don't know that it's the typical experience.
Anyway, I guess what I have gone somewhat off-topic to say is that my goal is to have quality subscribers who are interested in what I'm writing and will engage with it. Whether that's on Tapas or elsewhere.
And if that wall of angst doesn't make you want to read my weird story about sucking weapons-grade magical powers out of dead animals and my main character's undying quest to put those weapons in the hand of every man, woman, and child in the realm, I don't know what will!