It might be worth going into your analytics and doing a bit of research on what your most popular videos are, and how people are finding them (if you click on "traffic sources") - that way you'll have a better idea of which videos your subscribers are actually interested in watching - I think there's even a way to see which videos people subscribed from as well?
But yeah, if you take some time to figure out what your subscribers like about your channel then you'll hopefully be able to plan some videos that they'll want to click on