The Best-laid Plans...

So I've got a vague plot idea, and now I need to spin the idea into a real plot.I admit it: I'm not sure what's going to happen yet. But I do have a situation, four main characters, a villian (actually, a horde of aliens), and some of the plot set down.  Planning, of course, is my next step!  How am I planning?  Well, for me, I break it into parts.

Characters

I've begun planning detailed 'character sheets.'  If you've roleplayed, you'll know what a character sheet is: it's a summary of a character's strengths, weaknesses, attributes, and assets.  In most formal roleplaying systems, those are charted out in numbers; as a writer, it's a little more qualitative than quantitative.  But the idea is the same.  For example, my female lead: Cineraria 'Blue' Mazarine, present age 20, future age 32.  Where does she live?  Where does she go to school?  What does she like?  What does she not like?  What's her family like?  What are their names?  Does she have any quirky habits?  What are her strengths and weaknesses?  Does she have any enemies?  Who are her best friends?  What are her defining characteristics?  And what does she look like?

Races/Species

Since I'm working with more than humans, I need to figure what non-human species I have running around, and determine the limits of each.  This is sort of like a character sheet for the entire race, separate from the ones I do for my main characters (even if one of the main characters is of the race).

First, we've got aliens: Why are they invading Earth?  What do they look like?  How does their society function?  Their government? Do they have a religion?  How do they communicate?  How do they move?  What are their spaceships like?  What are their physical weaknesses?  Strengths?  How smart are they?  How dangerous?  What's their plan of attack?

And then, I've got the time travelers:  In this case, they're Immortals, but not like the kinds of vampire/highlander immortals you're used to: they're spirits who inhabit 'abandoned' (aka dead) bodies.  What are their weaknesses?  Can they be killed (yes, but it's difficult!)?  Obviously, they've been around a while, so why aren't they tiny and resembling ancient Sumerians?  Can they be physically hurt? (yes)  Do they heal faster than normal? (No)  Do they age? (No.)  Do people object to the fact that their loved one's body just got taken over by an immortal, before it could be buried? (Sometimes... depends on whose body gets taken!)  Do people worship them?  (Used to, but now most people don't, although a few fanatics still volunteer to surrender their bodies postmortem.  Although most volunteer bodies for a generous settlement to their families)  Has age made them mad?  (No)  What happens when their bodies die, if there's none around?  How do they take a new body?  Are they rich?  Are they political?  How is the world different with a set of immortals running around?  Can new ones be made?  How many are there, and what are their names?

Current History
Since I'm working with time, I'm also making myself a thorough timeline, including events that happen between the present and the hypothetical doomsday future we're trying to avoid.  (Hey, sounds cliche!  But then, most over-simplified plot summaries do.)  I also have to deal with difference between my characters as they are now, and who they will be in twelve years.  I've got to choose which major events will be included in the novel, and I need to decide how I'll put them in.  I'm toying with the idea of a flash-forward to start every chapter, but I usually add chapter breaks at the end of a novel, so we'll see. 

World Climate

Although I may not make a separate sheet for this, I might start jotting down notes on the politics of this world setting.  How do the immortals influence politics?  Are there any major deviations from current Earth?  If so, what?  Historical deviations?  How do most people view my non-human races?  What kinds of technology does the world have?  It's important to determine all the settings in your book, so I need to answer these questions for present, future, and even for the aliens.

Outlining

I'm not here yet, but my next major step will be deciding on a beginning and an ending.  How does the story start, and where does it end up?  Everything has to lead from HERE to THERE, and any scenes which aren't necessary to do so, better have a darned good reason for existing.  I might add that stories can have several "here"s and several "there"s, with each "there" being a resolution I want in the story.  For example, in this story, one "there" is that the aliens don't kill off all of humanity; another "there" is that my male and female lead get together.  Once I have a start and a stop, I can add in the major plot points: the big scenes that get you from start to stop.  With those out of the way, we can add in the filler material that holds the story together: plot twists, resolutions, minor events that contribute to the story, necessary background info, etc.  This is usually my last step immediately prior to writing, but many people take it forward past that and work in-depth planning, right on down to the chapter.

Planning is one of those things that seems to be unique to each person, and everyone has to find what works for them.  This is my way, but I wonder, what's yours?  Is there something that works really well for you?