-How do you prep your campaigns?
Overall campaign: quite a bit of prep ahead of time - complete rules overhaul, projected storyboard for what I'd like to run (and may get to actually run bits of), and worldbuilding: maps, history, major NPCs, weather and climate, realms and nations, etc.
Session by session: if I'm doing it right the macro side pretty much runs itself.
I just have to worry about the run-of-play stuff - narration, characterization of NPCs, the usual.
-How much do you write before hand, and how much do you improvize?
If I'm using a homebrew adventure I'll have made enough notes and maps ahead of time to run it; if I'm using a canned module then I do very little beforehand. I improvise more than my players probably realize, and have to when they left-turn - which in fairness they don't do nearly as often as they might.
After the session is when the real homework comes: offline and online adventure logs (the offline one has some DM-only info in it), occasional character updates via email, stats and records updates, etc.
-What is on your table during a session?
DM side: paper, writing implements, module (if relevant), notes from previous sessions/adventures, DM screen with lots of sticky notes, smartphone; and right nearby are rulebooks, minis, maps, tables and charts, etc.
Player side: chalkboard, minis, character sheets, player-side records and notes, tablets; and right nearby are rulebooks, more minis
Both sides: dice, snacks, happy drinks
-And how long do your sessions generally last?
4 hours, give or take; once a week, give or take.
Lan-"one of these days I'll scare myself by counting up how many dice reside here"-efan