I've split up my armies into 2 on several occasions (online MP Almohads), where I'd split my infantry from my cavalry, save 2 or 3 camel units. The cavalry would ride to the far right or left while the infantry would take the center or the other flank.

The enemy now has to divert his attention and split his army up. when the infantry attacks, the cavalry can either attack from the back or ride around and directly support the infantry. The camels are there to ensure no cavalry can make it to the infantry.

It works in several ways: it disorganises the enemies army (they'll probably put all their spears to one side which will hastily have to be returned to their original positions once the cav rides around them to support the infantry) and it leaves the initiative up to you most of the time. Your infantry is safe thanks to the camels, your cavalry is safe thanks to their speed.