Quote Originally Posted by Count Belisarius
With respect, the question is not specific enough for a concise response. My formation depends on what faction I'm playing. For example, with a phalanx army, I usually deploy in a single line to maximize frontage and minimize the possibility of getting flanked. With horse archers, I usually deploy in an inverted crescent with melee cavalry on the wings and try to suck the enemy's center into a crossfire. With a more flexible infantry army, such as Rome, I will deploy heavy on the wings with my best troops in the center and attempt a single- or double-envelopment. Also it depends on my enemy: I may deploy my missile troops forward if I am facing elephants, for example. Cannot really answer this question without more specifics.
you saved me typing