Treat every quest as if you've never done it before. I believe this is standard policy but I cant find the relevant post. Someone back me up or dispute me.

Yes.

You don't know there is an undead merchant boggs at the end of the processing quest.

Agreed, unless the quest giver tells you what to expect!

I've seen several people Meta-gamethe Smelly Dunwarren sewers because they assumed Adella Tyrell will tell them what to expect. SHE DOESN"T!

Yes, but actually there is some leeway. You -never- know specifics. But it's not crazy to say that the Mausoleum/Hoar Temple has a persistent problems with hauntings in the crypts, or that there's goblin slavers out in the Underdark, or that there's all kinds of Chosen in the sewers.

Agreed. But unless the quest giver -tells- you what the trouble is, you have to feckin clue what to expect.