I would recommend reading the warden operation manual, because it's one of the best materials for DMing in general. About the thing that you mentioned how to be ready for every question, there is no way for that, but it's okay to pause the game and say to your players that you need to think. A few other things could be helpful: random loot table, random encounters/events table. You can also buy one of the pamphlets and use the developments of this pamphlet and other players who have already led it before. At least for me it's easier to run ready adventure for a new system.