Looks like you've already covered collaborations, but for me what helped me get started was to get people I knew in real life or friends I had to subscribe and be active viewers. Try to have as high quality video and audio as you can, too. I must admit for myself I've been slacking on not uploading in HD, but I really should.
Also, I know it is tough sometimes to come up with entertaining commentary, but what I found that helped to be entertaining was to be more informative on the game and try to give info and be more tutorial-ish.
Editing is HUGE, especially when it comes to gamers. If and when you have dull moments in your videos, edit them out. Make a jump cut or some sort of transition, but viewers want to see the most fun, entertaining, and action packed parts of your videos, not necessarily the more dull parts.
I've been doing the whole gaming commentator thing for a while now, so if you have any more questions, lemme know!