Step 11: Accuracy
Think about your hopop system. What has the biggest potential variance? The bucking, nub ,barrel, and chamber all remain mostly the same between shot. They are however, interacting with a different BB every time.
That said the single most effective way to get better accuracy is better BBs. Buy high quality BBs of no lighter than .23g if you want stability and accuracy. For you snipers out there, use .25g BBs at the absolute lightest (.30 and higher are most common among snipers/DMs).
While it is true that heavier BBs decrease muzzle velocity, the decrease in air friction makes up for that within 50 feet.
Buy high quality BBs. KSC, Airsoft Elite, BBking, TSD, Bioval, and Goldenball bbs are some popular high quality BB companies. I personally use bioshot .25g bbs (for all my guns, from 340fps to 400 fps) because they are relatively cheap but still very high quality (and biodegradable).