For me the outline depends a lot on the particular story; more complex stories need more careful outlining. I've had one novel that I wrote with an outline that I could fit into my head, which just basically involved 4 or 5 phases of the story I knew I would need to work through.
Sometimes I find this approach useful: write a really short outline. Three to six sentences, just giving the broadest possible idea of what your story is about. An example, here's an outline of a novel I'm about to start working on:
* Petra (an agent for a futuristic security agent) is working undercover to expose a terrorist organisation; she discovers that they are planning to steal some military secrets. A mafia-like organisation also want those secrets; wouldn't it be good if we could get them to fight each other over them?
* The terrorists get the secrets, with Petra's help.
* Petra gets the mafia to attack the terrorists, take the secrets back.
* Petra's waiting to take them back from the mafia.
* Something goes wrong.
* Somehow she recovers the secrets.
As you can see, I'm not really very sure about the details. What are the secrets in question? (I'm thinking about a design for a prototype FTL drive) Why do the terrorists want them? What will the mafia do with them? How do we get them from one place to another. What's Petra's precise plan?
But, I don't really need to know all of these things to start writing. What I can do is start -- and then when I've written something that clarifies how a later part of the plot will work, I can expand the outline a little with the new information. If I get to a point where I'm stuck, I'll work on the outline more, because I probably just don't know where to go next (this is why I have outlines really; I find without them I get stuck and spend ages thinking about the next scene, when what I really need to be doing is thinking three or four scenes, or maybe even a few chapters, ahead and putting the stepping stones in that I'll need to reach those scenes...).
So basically, I start with a really simple outline, and expand it as I'm going along.