for gliders - before stalls or spins (to be considered before taking off! and again just before maneuver)
Height - not below 900 feet.
Airfame - check VNE
Security - straps tight, no loose objects.
(E ? if you have an engine, be sure it is stowed!)
L - Location - not over active airfield or habitations
L - LOOKOUT! And this is really important. In a glider first do a well banked 180 turn, and then reverse the turn 180 the other way; so other gliders won't think you just found a juicy thermal....