I clean the rifle and then lube the bolt and put a small amount of grease on the locking lugs- and make sure I get the chamber itself clean of oil and cutting residue.

Barrels will break in/wear in/season or whatever else you want to call it- as you shoot them. Most premium barrels are hand lapped and I do not do any break-in other than shooting. On factory barrels or cheaper aftermarket barrels there can be some pretty drastic chatter and machining marks. If those defects collect copper then I clean them simply because the built up copper will protect those spots and prevent the bullets from smoothing them out (and most likely cause accuracy problems).

I've never had a barrel that shot poorly at first suddenly start shooting great once it "broke in".