Well it depends on what your videos are about. Whenever I make videos about topics that are my opinions or something about YouTube that I have opinions on, I will get more comments. Or if you say I enjoy getting comments, or at the end of some videos - not all as this will annoy people - just say and remember to leave comments, I will reply to them all. I have 125 subscribers, but I feel if you reply to comments people will comment on another video because they remember that you replied the last time they said something. I have found though even with my small subscriber number - compared to bigger YouTubers - I get lots of comments which I simply have to delete from my video because people choose to use my video as a way of getting people to subscribe to them, which I really don't understand I don't get that many views on my videos...