Great tips, thanks for sharing! I'm seeing my numbers slowly creep up. At least 1 new subbie a day in the past week (and 3 yesterday, whoop!)
You're right: Promoting on Facebook is very effective. Twitter is good too. Also commenting on others' videos is making a difference, I wasn't doing that before. And I will be uploading a video response this weekend, and made sure I commented on that video to let the owner know.