There are a few things that help to drive the success (if subs/views/revenue are your measurements) of a YouTube channel. These are general things I've come to learn over time and by no means represent a complete "how to" list.
First, you need to have a host(s) that the viewers can connect with.
Second, you need to pick a subject that is of general interest. Gaming will be more popular in general than underwater basket weaving.
Another factor is the quality of the video. Shoot in HD, use good lighting, use good audio and you will find this will help. Poorly lit videos with horrible audio cause people to go elsewhere.
Then you have to network. Get creative on how you can get your videos out there. Work with other channels that have a common interest. Join a network that has a community of channels that will cross promote. Use discussion forums to share your videos. Facebook and Twitter can be great ways to build your audience. I've found Facebook to be especially useful. Drive people to your Facebook page through your videos and then be sure people know how to find your YouTube channel on your Facebook page.
Keep fresh content on your channel, Facebook page, Twitter, etc.
Take time to interact with your viewers. Promote new videos. Stick with it. It took me a year to find my groove and I'm still learning as I go along. It's a labor of love... if you don't love what you're doing chances are people will pick up on that.