Ah, that is a bit of a Holy Grail... or more like my mother's Caeser Salad dressing recipe - she's not giving it up, at least not till she calls it quit.
Google it, there's thousands of ways, as well as several Actions, or software applications that will do it for you. Finally, every Digital Photography magazine has regular How Tos....
I use something from a guy called Fred Miranda called
BW Workflow Pro. I don't have much time, and usually prefer to work up my own solutions in Photoshop... there are a lot of great ways that you can learn about on the Internet, or just search this site.
In the mean time, I dodged and burned a little, but can't say I made a meaningful improvement. I liked it better before I uploaded it, for some reason it just looks duller when it comes back at me over the internet. Not sure why...