The answer rather depends on whether you're asking about a crusader army arriving from Europe, or an army raised by one of the crusader states of the Levant; the composition will be different between the two, and I'm really only qualified to talk about the former.

As a general rule, western European field armies of the late 11th-early 13th century (which I take to be the period you're interested in) tended to consist of about 1/6 or 1/5 cavalry to 5/6 or 4/5 foot. The cavalry would consist of knights, sergeants (unknighted heavy cavalry), and perhaps some locally recruited light cavalry or horse archers. Archers and/or crossbowmen together with heavy infantrymen armed with shields and assorted weapons made up the infantry. "Regular people drafted in to fight" were never a very great part of medieval warfare, being almost solely confined to defensive actions (say, if the Scots have invaded and you need warm bodies NOW); and they certainly wouldn't have been brought 2,000 miles on Crusade. Basically, offensive actions were undertaken by professionals or semi-professionals: aristocrats, their retainers, mercenaries (loosely defined), volunteers, and the like.