To my understanding there are no hard and fast rules. Every scene is different.  I know some who love the one IBL and another light look. Others who aren't into that and prefer 3 infinite lights. Placement of those lights are up to you. I always find myself placing the IBL smack dab in the middle. The Infinite always in the upper left. Then you have to figure what each light's intensity and color will be. Use Gamma Correction though. Many will say that's a "must".

Oliver has some lighting tuts over at RDNA.