The great secret of aiming in airsoft is that you can fire from the hip and still get ridiculous numbers of kills and acceptable accuracy.
At a very slow 100 to 600 feet per second, bright white rounds, relatively high rates of fire relative to realsteel, and distances that pretty much never exceed 300ft ever if even 150ft, you are relying much more on the phenomenon known as feedback (see: http://en.wikipedia.org/wiki/Feedback
) than the precision of your sights. I challenge experienced players on this forum to yank the sights off their RAS setups and see how easy it remains to still do well in this game.
Zeroing your sights is pointless.
The post by Forever_kaos above pretty much nails it in that your number one priority when using your airsoft rifle is to have your hopup properly set for the environmental conditions that day as well as the weight, texture and quality of the BBs you are using that day.
With that in mind, you will have to adjust your hopup at nearly every game you attend. Even with identical environmental conditions, the soft materials of the bucking and the nub can and will shift and stretch over time even if you do manage to get a perfect setting for a given game. The one possible exception is R-Hop, but I'm guessing the R-Hop patch succumbs to some slight variance over time.