Nissan_Ranger is quite right. If you let the carbon that is introduced by the direct impingement system site overnight, it can cause small hiccups...and is much more difficult to clean off later. Even if pressing demands on your time are present, at the very least a once-over with the chamber brush and a quick wipe with a well oiled patch is imperative.
Marc...
What I do is pull the rear takedown pin, allowing the upper to hinge forward on the lower. I then remove the bolt without actually removing the charging handle (old habits from cleaning in the field).
Field strip the bolt (remove firing pin retaining pin, firing pin, cam pin, and bolt assembly). At a later time you will briefly remove the charging handle and then re-insert it.
Oil (and probably smear around) the following areas:
-Gas rings on bolt, bolt lugs, sides of bolt, cam pin sleeve (NOT THE BOLT FACE OR EXTRACTOR CLAW)
-Cam pin
-Bolt carrier rails (two top two bottom)
-Surfaces that bolt carrier rails bear on inside of receiver
-Top and bottom of charging handle (lightly)
By this time, you'll have the bolt carrier group back together (re-assembling as you oil avoids losing parts). Replace the bolt carrier in the upper receiver, and then cycle the action. You'll also be doing your test after assembly...you do that after every time you strip the weapon, don't you? This will involve more cycling of the action. All of this cycling will help to evenly spread that fine coat of lubrication to all the appropriate places.
Essentially what you've done is applied a fine coat of good quality gun oil (or teflon loaded CLP) to the areas where metal on metal friction may occur.
Dumping a pile of oil onto the components and then wiping it off is messy...I will normally just semi-saturate a 2"X4" patch with gun oil, and then smear it onto the appropriate areas. The exception to this is the gas rings and the bolt carrier rails. They benefit from a little bit more oil.
All of this said, do not over-lube. Cold temperatures will make that lube like molasses, and if your weapon is dribbling oil out of every orifice, it will attract so much grit that it'll feel like you've got gravel in between the bolt carrier and the receiver.