Excellent Strobist post...

[sando]

...if you're into Flash and don't read the Strobist site, then you suck. Fact! :P :D

This is a great post he made about balancing flash and ambient.

http://strobist.blogspot.com/2007/09/lighting-102-33-balancing-flashambient.html

[Curtis N]

This kind of stuff is easy for some and not so easy for others. If you find yourself in the latter category, then the Lighting 102 series on Strobist is for you. He goes step-by-step, one brain cell at a time.

Even if you find this learning curve steep, it's worth climbing. Every flash photograph is two exposures in one, and when you learn to control both, you have the power to do amazing things.

Personally, I tend to go about this process the opposite way. I figure out how to expose the ambient first, then dial in the flash. Because that's the way the camera works with E-TTL. There's no right or wrong, and when you understand the concepts you'll soon figure out what works best for you.