Prophetic visions are difficult to handle in a roleplaying game. If you're writing fiction, you can make sure that the prophecy maps directly on to later events. But a game is open-ended and events can take unexpected turns, which can quickly lead to positions in which your carefully crafted prophecy is not only proved false, but also patently ridiculous. Yet prophecies remain a powerful staple of fantasy literature and so it's natural to want to include some form of them in your games.

One solution is to frame prophecies vaguely. In the manner of Nostradamus, a suitably vague prophecy can be interpreted after later events as having been about those events. The disadvantage here is that you can't draw those links before the events transpire - the prophecy only becomes "clear" after the thing it supposedly discusses actually happens. Which is kind of useless and lame, as prophecies go.

Another approach is to make the prophecy of the "this will come to pass unless you do something about it" type. This gives the PCs the chance to react to the prophecy and try to prevent it from happening - assuming it's the sort of thing that they don't want to happen. You can craft happenings and NPC actions leading towards the prophesied event, and modify them based on PC actions, giving them a chance to influence the fate of their world.

This is the safest approach, since you just know that the players are going to mess up whatever you have planned.

Transcript

Anakin: Padmé, I've had nightmares every night since we met.
Anakin: I saw Qui-Gon's doom, his robes wet with blood. But I didn't dare say anything.
Anakin: I saw your Senatorial ship blow up on the landing pad. But I didn't recognise the significance.
Anakin: I saw my mother dying in my arms. And I couldn't stop it.
Padmé: Maybe you should take some time off. You've been under a lot of stress lately.
Anakin: There's too much work to be done.
Padmé: I can help.
Anakin: You're helping already. Your protest group needs to overcome the Senate's inertia.
Anakin: When I find the Sith Lord, we'll need to act faster than the bureaucracy can.
Padmé: Oh. I was thinking more like a shoulder rub.