Focus Global Community

What rules do I need to focus on in order to create the best viewable website for all?

Challenges:
There are multiple browsers...
People use multiple monitors, heck some use their TVs...
Some people are color blind.
What is the best font that is clear & readable
What's the best placement for ads?
What is the best format to use to make a blog readable?
How do I prevent tables that collapse & "write" over themselves when viewing in alternate browsers...
What's the best placement for photos & graphics?

I know that I have hit quite a few here...
Is there a good how-to text or video? (video there's another challenge)