This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
From: Mike Iglesias <iglesias@draco.acs.uci.edu>
Here's a simple rule to remember which direction to turn the pedals
when removing them from the cranks: With the wrench at the 12 o'clock
position, turn the wrench towards the rear tire. This works for both
the left and right pedal.
The left pedal has left-hand threads (tighten counter-clockwise), so it is
the opposite of the normal right-hand treads found most everywhere else on
the bike.
 
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