I understand that everyone here is an avid player, and I don't mean to disrespect anyone, but there's a trick in Heroes 3 regarding magic... In battle, you can open the spellbook twice in one turn...
It's easy and doesn't count as cheating... Basically, during the battle, you press the "spellbook" key (usually 'c') and hold down the button, and then with the mouse, you click on the image of your Hero (in the upper right corner, on the horse icon, for those who don't understand). This also opens the spellbook... Thus, we open the spellbook twice in one turn!