Maybe what I will say is obvious, but
1. Do something new, be unique. Don't copy Grian, Scar or Mumbo or whoever else you watch, because no one needs an other copy of them. Find your own "thing".
2. Do it good. Give some effort, a lot of it. Work on your voice, your presentation, edit your videos so they will be entertaining, and not just unedited gameplay with ocasional boring comments.
3. Then goes your typical promotional stuff like thumbnails, consistency, being a part of community (not begging for views and subs! That's different!)
But this 3-rd part will not work if you don't have 1 and 2.