This is a great article about YouTube:
The YouTube Laugh Factory: A Studio System for Viral Video
Rule 1 - Make a lot of content. A lot.
Rule 2 - Target a niche. The article has some good non-obvious ways to do this.
Rule 3 - Connect with your fans. The internet is about conversations. This applies to all aspects of your business, not just YouTube.
Rule 4 - Collaborate - Try to connect with the niche/market leaders and see how you can work together for your mutual benefit.
Rule 5 - Optimize - Obviously essential. Do it right.
Even though the article is more about comedy and music, it till has a lot of great ideas that you should be able to adapt to your niche.
Onward and upward!