...not only preparation, also good practices while the contest is running:

• Task overview in Melange: After clicking "columns" at the bottom and adding the "Modified on" column, I often use it in combination with status "NeedsReview" to check for stuff that's getting close to the 36h deadline for reviews.
• Check daily for new "Unapproved tasks" (which were not in the system from the beginning and planned to get published over time, but were added recently by other mentors and should get accepted and published by org admins)
• Org admin to weekly gather stats on open/claimed/closed tasks and publish them as a diagram (2013 example).
• Send summary after first week to wikitech-l (2014 example)

• Importing tasks from wiki planning page though mentor has not created account in Google Melange yet: Set yourself as (temporary) mentor and set real mentor as [prefix] into task summary
• Creating recurring/clonable tasks: Use suffix in title of recurring tasks like (03), (04) otherwise email threads hard to distinguish. Consider using the bulk uploader.
• Daily routine on https://www.google-melange.com/gci/dashboard/google/gci2014#all_org_tasks
  • Check age of tasks in "NeedsReview" state (<36h intended)
  • Check number of tasks via in "Open"/"Reopened" state (>50 intended)
  • Check for new tasks in "Unapproved" and "Unpublished" state and review/publish/subscribe to them
  • If recurring tasks exist, order by title to check if enough are still open and if you should "publish" the next one (if using suffix number in a title) that's been unpublished so far.

Created https://www.mediawiki.org/wiki/Google_Code-in/Admins and linked to it from https://www.mediawiki.org/wiki/Google_Code-in
Improvements, edits, feedbacks welcome.

I read the page yesterday, it looked rather comprehensive.