Also, positioning, gems and research choices can help a bit.
-By denying a mage gems, you limit what they can cast; By giving them a certain type of gem you prejudice them towards casting spells that "use" that gem (if only as part of the fatigue calculation).
-Mages near the rear won't cast enemy targeting spells where the enemy is out of range. Mages near the front may wind up engaged and be unable to cast. A mage can be limited by selecting five spells then "Retreat" as the next action.
-You can't cast it if you haven't researched it. If there's a spell you just
hate, simply choose to pursue other schools of study.
None of these is a terribly good answer. You get to script five and then hope for the best. I occasionally find it advantageous to put my mages where they can't accidentally hurt someone I don't want to lose
~Aldin