I only promote the videos I really like. The last 2 I made I didn't promote at all, in part to see where my channel was at on it's own, and in part because I don't like them that much and don't even really know where to post them. That's why the viewcounts are pretty dismal for my recent videos.
Some of my other videos took off with little to no promotion either, though. I wish when that happened it translated to more subscribers, though. I don't know how 1,000 people watched a video and then didn't click through to the channel for the most part (it's like a 1% conversion rate or something sad like that). But hey, I'm glad those videos did well...
The next video I release I'll promote a lot, because I think it'll be really funny. It's not even made yet, though, so we'll see!