This kind of foretelling is the opposite of inescapable fates. The future is an infinite number of paths stretching forward from Now. Any time someone peers in to a crystal ball or has a precognitive vision they see the most likely future. It will happen if everything remains unchanged, but there is plenty of time between now and then for things to change.
This might be a more modern view of the future-- a future of variables and probabilities. Future as an equation where the inputs are fuzzy and prone to change.
These kinds of visions of the future can be specific and visual, like dreams or scenes in the mind. They could just as easily be vague like Future as Fate predictions, something like "misfortune will strike your friends" with the understanding that the misfortune could be avoided. But, because Future as Fate can only give these vague kinds of predictions, why not be distinct and present visions of future possibilities as rich visuals.
This kind of foretelling is much more useful to players because it is about gathering information to help make choices. Why find out a friend is going to die if you can't change it? This vision of the future is more active and empowered. Players find out about the future like scouting a foreign country.
There won't be a single, elegant solution like Zak's for this kind of future because there are so many variables, but I think we can at least come up with some guidelines
Which Part of the Future to Show
Because the possibilities are open it becomes hard to decide what part of the future to even show. How far ahead should be shown? And what about physical distance from the seer's current location?
One thing to keep in mind is that if a future path depends upon decisions, each decision you assume for the players makes a particular path less and less likely. It might be a good rule of thumb to either show the future as the outcome of one particular choice or show the future up until the next big decision point. The first will help players decide if that is in fact the choice they want to make. The second will prime them for the upcoming big choice, and hopefully build dramatic tension.
In general, though, a week ahead would seem quite far, a month probably the limit for things revolving around the PCs (See the next way to foresee for grander destinies). As for physical distance, again a week's travel would seem far. But this still doesn't lay out what choices a vision of the future would show.
Probably the best guidance on what to show is to remember that players will want to use it to inform them. So the PCs' present situation is a good starting point:
The Players Have No Plans
If the players are in a safe place and have no particular plans it might seem odd that someone would be looking into the future. But there are things besides the PCs themselves that grant visions. A place might grant visions to those that sleep there. Fevers, drug use, or magic items all might grant a glimpse of things to come.
If players have no particular plans, this kind of DM granted vision can essentially act as an adventure hook. These may not be about choices so much because you won't be sure that players even want to get involved. The choice is, in effect, this thing is going to happen do you want to stop it, or maybe take advantage of it? But a vision that involves strangers or strange places will amount to the same thing as hearing a rumor. To be more magical and interesting these visions should probably provide a glimpse of something happening to the PCs, their friends, or their belongings. Here is the simplest chart I can imagine to help you with this:
Example: Someone hated by the PCs is ravaging a familiar object out of greed.The Party is Heading on a Journey
You see the orc One-Eye who killed little Bobby the link boy last session. He's in a 10'x10' room sweating as he stoops over something, hammering. You see it now, it is the Great Crown you've been searching for. He's hammering on it to get out the rubies and the beautiful piece of art is mangled before your eyes.
For wilderness travel you can roll encounters and weather for a week ahead of time and relate that to players. This will let them make decisions about what to bring and how to prepare for this particular journey. Likely decision points might include which of several routes to use, or, after a dangerous encounter-- whether the party should even continue.
The Party is Heading into a Dungeon
A dungeon zooms things in considerably and it becomes difficult again to decide what part of the future to show. But there are a few focuses that players might be interested in knowing about. You could either decide which of the following is most important for this dungeon, or roll randomly to determine which of these to show them:
1) A Terrible threat. Choose the most dangerous foe the dungeon holds in store for this particular party. Show them fighting it and, if defeat is likely, show them getting slaughtered in vivid detail. This is one of the few times you might impress on players the lethality of the game and the real possibility of death without them suffering the consequences. A party might take this as an opportunity to plan carefully to take on this foe, but they also might feel empowered to just run at the first sight of it, if they've already seen themselves getting slaughtered by it.
2) Many Challenges. A Rocky-like montage of difficulties, especially terrain-based is another option. Show the PCs using ropes, iron spikes, burning oil, string to navigate mazes. This would basically serve as an overview to help players prepare. In some ways it would function as the Pre-Mapped Dungeon, but the players don't necessarily know where the images they see are located within the dungeon. It is also a way to show them many smaller scale challenges instead of a single large one.
3) Treachery. A Preview of desertions and double-crossings from factions in the dungeon and/or hirelings.
4) A Dilemma or Big Choice. There might be one particularly important choice in the dungeon, for example, releasing a bound demon or not, or starting up magical machinery. The vision could show the choice being made in one way.
A Player Wants to Know the Outcome of a Particular Choice
While the archetype of those that can see the future is often about getting visions you can't control, I think it will be more interesting to everyone if the visions are useful to players. For that reason, I don't see anything wrong in just asking the players involved "What are you interested in seeing?" They might answer any of the things we've mentioned above ("I want to see what happens if we take the shortcut in the woods," or "I want to see who will betray me in the caverns.") or they may ask about turning the handle one the big, creepy door to the left. This can essentially defang traps, but if your traps are set up more as obstacles anyway, knowing what happens won't necessarily tell the party how to get through the door safely. Also, spells, magic items, and precognitive abilities will most likely have limitations on frequency of use that will prevent layers from avoiding all uncertainty.
The next way to foresee is really a subset of both these first models. But the Future as a Web is different enough that I think it warrants a separate look.