Most of this information is available on the troop information page/windows. Tells you what kind of terrain they are good on, defense strength, attack strength, and stamina (how hard it is to kill them).
The strategy is in using that information to plan your attacks, and prepare your defenses. Not classified, but more a matter of individual preference.
Also, your strength is altered by many things: honor level, university research, troop updates, hero level, et cetera.