"To know your enemy, you must understand his strengths and his weaknesses. His disposition, his resources, his temperament, his will. Where does he find his advantage, and where does he falter? Study his past campaigns, his typical formations, the commanders he favors, and the morale of his troops.
Observe his movements closely. Does he advance swiftly or cautiously? Does he concentrate his forces or disperse them? Does he protect his flanks or leave them exposed? Does he react to feints, or does he hold firm?
Furthermore, consider his internal affairs. Is his ruler wise or foolish? Are his people loyal or rebellious? Is his treasury full or depleted? Is his supply line secure or vulnerable?