Alacrity rating reduces the cooldown of all abilities (apart from a select few, and it does nothing for internal cooldowns) regardless of their activation time, it also affects instant abilities by reducing the global cooldown time. Also it increases the amount of resources you regain per tick (this obviously is not the case for warrior/knight, who does not regenerate resources like the other classes).
For other tertiary stats (alacrity, surge, accuracy etc) you need 760 accuracy rating (this is necessary, non negotiable) the rest can then be filled with surge and alacrity according to your preferences. Someone probably wrote something clever about this on Dulfy.net