1 ACCEPTED SOLUTION
You can set a default order with a user preference, but that doesn't preclude users from clicking the header and choosing their own sort field/order.
The easiest way I know to set the default preference is to set it yourself, then go to User Administration> User Preferences, sort by date updated (descending) and find the entries you just set/created (example below where I sorted the Task SLA related list on the incident form.)
Open each record and remove the user (System Administrator) and check the System field, then save. Now you have a default setting.
http://wiki.servicenow.com/index.php?title=User_Preferences
