One of the questions, in some form or another, that I see when people are starting to get really into GMing is on how many plot hooks should they have prepared at any given time. The idea being that they don't want to force their players onto an adventure, and so they want choices to be available. This then brings up the fear of "but what if they ignore the plothook? all that wasted work!"
Today I want to talk about this, and some tricks/ideas for how to be ready and not get caught unprepared.
First, The Answer
Before going into the how, I'll give my answer to this question. A GM should have as many plot hooks ready as they feel they can manage. If possible, the GM should have infinite plot hooks more or less ready to go at any moment.
That Seems Impossible...
You're right, infinite plot hooks is impossible. However, do things right and your players don't have to know that you're not doing the impossible.
The 37 Plots
In storytelling, depending on who/what you ask you'll find 37 unique plots. That's it. In the entirety of human story telling, from countless years and millenia of telling tales, we have 37 unique plots. That is an insanely small number, especially when you consider that over three hundred thousand fiction novels are published (or self-published) every month. Even more insane, most modern novels have more than one of those unique plot items in them.
The idea of their being thirty seven plots shouldn't scare you. Instead, it should be freeing. Why? because it is absurd to try to be unique, all those stories are done, instead you can just focus on making things fun.
The Standard Adventure Plot
Of those 37 plots, most RPG adventures boil down to one plot at its most basic. The PCs go somewhere, they kill some people, and they collect a reward. In D&D this is a classic dungeon crawl, but could also be stopping a Drow raiding group from attacking some surface elves. In L5R this could be Emerald Magistrates making a bust, or it could be stopping bandits on the road. In Star Wars this could be a Rebel strike group hitting an Imperial Facility, or the smuggler getting his cargo back. Doesn't matter, it's a simple chain of events.
Let The Players Do The Heavy Lifting
If you let them the players will do a lot of your work for you. When they go to look for information for things to do you can simply ask them "how are you trying to find this information?" In response to this your players will have a few responses. Perhaps they're checking with some friends or contacts. Perhaps they're collecting rumors in the courts and palaces of the nobility. Perhaps they're asking the bartender of the local inn/tavern for rumors. It doesn't matter, because whatever their approach is going to give them a set of limited answers.
The interests of a noble are going to be different than those of a contact and both will differ from the bartender. When you ask the bartender what he's heard, he is going to talk about problems that affect the common folk. This is where your players may find out that Farmer Brown is having problems with Goblins raiding his livestock, or that a couple of the local kids have gone missing exploring the caves near Cloud Lake. The noble courts are likely to have tales of intrigue and high society, places not paying taxes and raiders preying upon key roads. The contact will have information related to their direct work.
But How Does This Help Me?
Remember how I said there was one standard adventure plot? Well, what makes Adventure 1 different from Adventure 2 is the skin it wears. You don't need to have a bunch of convoluted plans ready to go. All you need is a reason for the PCs to go somewhere, a place for them to go, a thing they're going to get in return, and opposition for them to face. After that, your players are going to do the hard stuff of determining their approach and the tactics they use.
So on Session 1 when the players go looking for something, and ask the local bartender, you talk about the farmer's woes with goblins and mention some reward (fame, money, prestige, the farmer's ancestor's magic sword, etc.) The players go out, fight some goblins, and have an adventure easy peasy. Then they look for whats next, and go to their contact. The contact tells them stuff, they go they fight, they kill, and done.
That Seems A Little Plain
It does indeed, and that's because it is. The thing is, for a quick answer it works. As you practice and GM you'll get better at reasons. You'll also get better at making them more exciting, but starting simple is a great idea. Why? Because you can always add complexity later.
Session Break: Simple -> Complex
Eventually you're going to hit a session break with the PCs about to do something. Maybe they're looking for the goblins raiding Farmer Brown's place, or maybe they've just collected information on their follow up job. The point is you now have the players right where you want them. They have a task in mind, they're going to do it, and you know what it is.
Now you can take the break to add complexity to things. Perhaps the goblins are raiding Farmer Brown because they've come into the employ of a Dark Wizard, or there is a tribe of Orcs nearby that are making them do it and pay tribute. Maybe the kids are going missing by Cloud Lake because a group of gnolls are nesting their and raising their young, The kids aren't dead, but the gnolls are raising them like one of their own now and the kids need to be rescued.
The key is, in session you stay fast and light on your feet. Have some things prepared, but be ready for your players to throw you a curve ball. End the session with your players having set their own course. Then use the break to plan around the course the players have set.