if you want to help break in your upper before you get it out to shoot it, its a relatively simple process
step 1: disassemble & clean the upper receiver and the BCG of all lube. use something like birchwood's Gun scrubber. or Non-Chlorinated Brake Cleaner (like from the auto parts store).
Step 2: reassemble your upper - WITHOUT ANY LUBE AT ALL. you want it bone dry. then put your upper back onto its lower.
step 3: pull the charging handle back and release it like if you were loading a round. No mag, etc.. this is a while the gun is empty process.
Step 4: repeat step 3 - 200 times.
step 5: disassemble, give everything a quick once over with your favorite gun cleaner to remove any schmoo (yes thats a technical term! ) created during the wear in and then lube everything properly and reassemble
by manually cycling the action this way with no lube,it just smooths out the mating surfaces where the BCG and the upper receiver make contact during operation.
you're essentially lapping the surfaces just like would happen when under recoil - just knocking off any possible burrs, chatter marks, etc - without having to waste any ammo.
HTH