You also might want to flesh out locations a bit (and use them some other time when they don't get used) and some NPCs. Simple stuff like what the place is, who is there, and what's going on. Maybe why, if the question makes sense. That way, when the players decide to go prepare for their trip, or go ask random people in the tavern for information, you already know what those places are and possibly what they can learn.
So the tavern has a tavern-keeper, some sort of entertainer, a traveling apple merchant, and maybe a retired adventurer or other local who is just there to drink. Make up a stupid name for the business, and you're good to go.
Off the top of my head (based on what I feel like would get asked, or the people would know): The tavern keeper mostly keeps busy with work and isn't aware of what's going on outside of that, but does know who is around and can point you to someone who can probably answer their questions if you buy something. The entertainer has stories about things that happened long ago, and will tell them as a song for a silver piece, and the story is 70% true. The merchant doesn't have anything useful, but can trade information from the PCs for information about surrounding towns and areas they avoid. The local can tell you about local goings-on if you buy them a drink, which was probably the price of the tavern keeper telling you who to ask in the first place. I don't know if you'd write anything down for that, depending on how good you are at remembering why you did things, or what your shorthand notes meant.
For larger locations, figure out how people and goods get in and out. Also, what do they use for sewers, because PCs really want to catch hepatitis/cholera.
You don't actually need to keep the players on track. Just have a back-up plan, and use money as an incentive to do what you want them to. They get paid however much gold for exploring the dungeon and bringing back whatever, or they don't do that and don't get paid. They could rob a house, but the local thieves' guild wants their cut up front (in case they get caught), or they'll get ratted out to the guards. There's also someone who wants them to go find someone in a wilderness location, which leads to a different plot.