Gaming once a week, the plan normally goes as such:
At Some Point During Six Days: Write the session, figure out if I need to do stats for anything, plan out the NPCs and monsters if there will be combat, and leave a bunch of stuff vaguely defined for when they do something I don't expect. Pick out music that will be played for specific scenes/battles/people.
At Some Point After The Session Is Written: Double-check stats and make sure I didn't make the encounter too hard or too short. Also, add in encounter saves as I always forget those.
That Morning: Read over session again, make little nitpick changes.
That Day: Print out my notes.
That Night: Joke around with players, steer them into the game, game for about 3 hours, then go out for dinner.
After The Session: Jot down anything really important that I need to remember.
Some sessions have special additions, like custom remixed music or special voice-acted 'cutscenes,' but those take forever to do so they're not always used.