3x5 cards, chapter by chapter, at least 3 chapters ahead at all times. Additional 3x5 cards, sometimes color-coded, usually not, to give character sketches, scene ideas, timelines, battle-plots (though I usually use a specially-designed Excel spreadsheet for this for my space opera), etc. I also have a vast spreadsheet-based map of locations, characters, fleets, events, fleet movements, etc, which gets updated usually on a chapter by chapter basis.
For my first novel I also had a very intricate size/volume/weight/O2-CO2/buckling force spreadsheet since I was dealing with hard SF issues involving all of those.
If I need details on a ship design for my space opera I have an integrated spreadsheet for designing every major detail of anything from a ground unit to a starbase, hundreds of pre-generated designs to draw on from 15 years of running a space opera game, and over 500 single-spaced pages of internally-consistent technologies taken from the game I used to run. I can run full-scale fleet battles with thousands of ships on each side in seconds, generate a new alien race on the fly (including design parameters and preferences, numbers of colonies, etc., etc), and generate thousands of new star systems in minutes if I need to (complete with most data needed for information on the system and any individual planet). I have space opera level data on a volume of space over 6 thousand light years on a side currently and several more unconnected areas of equal size.
All that data is accessible via Excel so I can call it up anytime I need to (a lot of it really needs to go into an Access database though).
I outline major events and chapters on 3x5 cards, wing it through minor events, and consult my data sheets really only when I absolutely need to.
Major characters often get 3-5 cards all to themselves, minor characters usually only one.
I've also been known to use the app iCard Sort on my iPad to do 3x5 card outlining. It works great.