Sticking to a single niche
HA. Maybe in another life.
Popups asking you to subscribe
Do unto others what you have them do unto you.
Email lists
In my experience too often email lists are crap - people do them because they 'should' but don't actually have anything worth offering.
Video
I may be in the minority but I know I'm not alone in shunning video content for the most part. I'm not into vlogs. I'm a word person. Unless there is a damn good reason to present it in video form, I want to consume your content in written form, thanks. In my experience working in online media, too often people do video for the sake of it, not because it's actually the best medium for the specific content.