It is easy to see medieval warfare and politics as being long on activity but chronically short on reflection. To misquote the 1970s feminist rallying cry, it is pretty obvious that hairy, unwashed medieval warriors needed strategy every bit as much as a fish needs a bicycle. Or at least that is often our unspoken but default attitude. This is lazy and patronising thinking, and potentially very misleading.
One of the defining features of Crusader warfare was the heavy cavalry charge, a tactic borrowed from the Frankish knights of Western Europe. These heavily armoured horsemen, armed with lances, would charge in tight formation, aiming to break the enemy lines with their sheer force and momentum.
A siege is a military blockade of a city, or fortress, with the intent of conquering by attrition, or by well-prepared assault. This derives from Latin: sedere, meaning 'to sit'. Siege warfare is a form of constant, low-intensity conflict characterized by one party holding a strong, static, defensive position. Consequently, an opportunity for negotiation between combatants is common, as proximity and fluctuating advantage can encourage diplomacy. (Source : https://en.wikipedia.org/wiki/Siege Wikipedia)
An ambush is a surprise attack carried out by people lying in wait in a concealed position. (The concealed position itself or the concealed person(s) may also be called ambushers.) Ambushes as a basic fighting tactic of soldiers or of criminals have been used consistently throughout history, from ancient to modern warfare. In the 20th century, an ambush might involve thousands of soldiers on a large scale, however, in the Crusades, it wouldn't have consisted of as much.