thats a great question, where to start...
how about where i started !

image/mode/lab
image/adjust/curves

beyond that , i'm not too sure. Like i said on that previous post, my curve tends to be the same each time with some minor variations. There's just this one little trick that you have to use in order to get the curves to really work tho. Shall i share? or maybe i should wait and see if anyone can figure it out... 'specially you Alpha... ;)