This video from a ex-military sniper is one of the best I have seen when it comes to the proper alignment of a rifle scope. It does not go into detail as far as making sure the scope is aligned properly as much as it describes the relationship between the shooters position and the eyepiece.

This is good information from the folks at Valhalla Armory. I have one of their Ultimate AR-15 scopes and it has been worth the money. It does not compare to my EOTech but then again it's much less money.