There are three general tricks to working with the AI:
1. The AI often acts around what it thinks you want to do. If you're advancing for a pitched battle, it will often join (unless it thinks it's suicide). If it thinks you'll join a pitched battle, it will often push for one. If you want to avoid the AI charging blindly, pull back and they'll often do the same.
2. The AI likes to split stacks to prevent attrition. It will generally try to stick to your rough location, but will rarely stand "on you" if doing so would cause you both to take attrition.
3. The AI likes to claim good defensive ground, especially if it's small. Sometimes it's reluctant to give that ground up, especially if the enemy has men-at-arms that do poorly on that terrain.
Some of this isn't necessarily true during crusades, though. Seems to me that in crusades, the AI lords are all competing to be the ones who get the highest warscore, and that can lead them to make foolish mistakes. Somewhat historical, that!