All warfare is based on deception. Therefore, when capable, feign incapacity; when active, inactivity. When near, make it appear that you are far away; when far away, that you are to lure him; feign disorder and strike him. When he concentrates, prepare against him; where he is strong, avoid him. Anger his general and confuse him. Pretend inferiority and encourage his arrogance.
Thus the highest form of generalship is to balk the enemy's plans, the next best is to prevent the junction of the enemy's forces, the next in order is to attack the enemy's army in the field, and the worst policy of all is to besiege walled cities.
It is imperative to contest all factions for complete victory, so the army is not garrisoned and the profit can be total. This is the law of strategic siege.
Do not engage an enemy more powerful than you. And if it is unavoidable and you do have to engage, then make sure you engage it on your terms, not on your enemy's terms.