Stuff To Study Up On

There are weak points in any DM‘s understanding, and here are some of mine:

Polymorph spells often vary according to game and are varying in what they allow. Make sure I have a good idea of what is allowed.
Illusions need a consistent ruling; I am going to go with the one from Basic Fantasy because it seems consistent.

I need a good handle on the combat sequence, especially surprise and initiative.
Grappling rules!