The Devilsaur Eye is a trinket awarded to a hunter for completing a chain of quests that leads into the Sunken Temple. This item increases attack power by 150 and your hit rating by 20 for 20 seconds upon use. The way to maximize the effect is to use it and cast Rapid Fire at the same time. Here is the macro that does this:
/use Devilsaur Eye
/cast Auto Shot
/cast Rapid Fire
Rapid Fire cooldown takes roughly twice as long as the Devilsaur Eye. The damage this macro does is equal to using roughly 1500 mana with serpent sting and arcane shot with auto shot running.