Capacity to crouch was added with warband 1.150's update giving troops the chance to duck behind low areas, deployed pavises or even their own mounts if they dismount and can provide considerable shelter from incoming arrows when under barrage.
Ordering your archers to ignite arrows will slow their rate of fire, but provides a boost to damage delivered. Additionally this makes it considerably easier to track where your arrows are traveling.
The deployable pavise shield acts as portable cover from missiles and the like. Best used by crossbowmen, including yourself, against factions such as the Rhodoks or the Khergits. If you are equipped with a deployable pavise and press "G", the pavise will be deployed and you can take cover from enemy range weapons (Video).
Credit: The Mercenary (scripting), Papa Lazarou (animation)
Spear bracing allows you to brace your spear against incoming cavalry. When the horse collides with the spear, it will nearly always die and hence de-horse the infantry on top. Best used when fighting enemies from cavalry based-factions, such as the Swadians or possibly the Khergits.