I've been doing Youtube for more than 4 years now.
And these are the basic rules:
-Find a game that you'd like to let's play, if it's fun for you then your commentary automatically sounds happier.
-Don't start Youtube for the reason that you wanna get money/subscribers/likes.
-Take your time with editing your video, at the beginning you don't have to be a pro at editing but at least put some effort into it.
-Creativity is a big part of making videos. Adding some funny stuff (pictures...) into the let's play will help you aswell.
-Do let's play togethers with other youtubers or friends,
-Have good equipment. You don't have to buy a 10 million headset, but buy a good one. Also don't film let's plays with your camera.
-Respond to your subscribers if they have questions.
-Block the haters and don't argue with them.
My channel is
here. There might not be too much on it, but if you watch the videos you will see what i mean with the creativity and the picture editing, especially on my DayZ videos.
Hopefully this helped.