If it slides; grease it. If it rolls/rotates; oil it. Or at least, that's what I was always told.
Using the Garand as an example, I use oil on maybe 1 or 2 places (can't remember offhand), but I use grease on everything else. I prefer Mobil 1 synthetic (the red stuff). I apply with with a children't medicine syringe (they give them away at the pharmacy) and then spread it around into a thin layer with a small, hobby paint brush.
But, oddly enough, I don't use the same train of thought on every firearm (maybe I should? :think: ). On the AR's, I use CLP on everything (in light coats).
-WRM