Classes - which are allowed?
Races - which are allowed?
Pets (eidolons, phantoms, constructs, purchased animals, etc.) - is there a maximum number allowed? Are pet classes frowned upon?
Alignment - enforced? For example, is a neutral paladin allowed? Will a good cleric lose all abilities from, say, using poison?
Class stereotypes - enforced? For example, will clerics be expected to heal and Druids expected to be nature experts?
X to Y - frowned upon? Examples include Nature's Whispers (Oracle revelation), Orator (feat), and Student of Philosophy (trait).