The undead move silently. Think about this when listening at doors, etc.

There are many monsters that suffer penalties when fighting in full daylight, including orcs and goblins. Hobgoblins, however, do not suffer penalties in daylight.

Many spells that affect the mind, such as charm or sleep, do not affect undead. Poison doesn’t, either.

You can communicate, at least at some level, with many different types of monsters. This can avoid deadly and costly combat and may lead you in beneficial directions you may not have expected.

Poison is most often deadly on a failed saving throw. Never engage monsters that have poison attacks at melee (hand-to-hand) range unless you have no other choice.

Monsters, especially those that operate in groups like orcs, goblins, kobolds and hobgoblins, will use tactics, strategy, and lessons learned to improve the effectiveness of their defenses and methods of attack.