stiff, light, quick handling.
As for Geometry, typically you're looking at bikes with short chain stays, short wheelbases,fairly steep seat and head tube angles.
You're also going to want the bike to set up in an aero position, so bikes with long head tubes that are intneded to setup for an upright position are the opposite of what you're looking for.
Of course there are mutiple ways to skin a cat, and lots of geometry is personal preference (for example Lemond always advocated a pretty laid back geometry.) so all the above is a pretty gross generalization.