Well the things that have worked for me are consistent uploads (I do 2 a week). Learn as much as you can about good editing, production value helps. I also invest heavily in good SEO practice and I use tube buddy to assist with that. There's no over night trick, you have to dig in and bed down for the long haul. Some times you get lucky. I mean, for some reason I got 290 subscribers off the back of a single comment I left on another video!
Most youtubers give up before reaching their first 100 because it's arguably one of the most difficult milestones to reach when you're new, someone un subbing when only have 30 in the first place can feel devastating. Just keep going and strive to constantly improve your content, find your voice and style, be consistent, good SEO, and upload quality stuff. That's what seems to be working for me at least. Good luck ☺[DOUBLEPOST=1499842861,1499842715][/DOUBLEPOST]
Thanks Crown ☺