Most orderly trial involving African dictator (7)
I believe the answer is:
tidiest
'most orderly' is the definition.
('tidy' is associated in meaning with 'orderly')
'trial involving african dictator' is the wordplay.
'trial' becomes 'test' ('test' can be a synonym of 'trial').
'involving' indicates putting letters inside.
'african dictator' becomes 'idi' (Idi Amin).
'test' enclosing 'idi' is 'TIDIEST'.
(Other definitions for tidiest that I've seen before include "most trim" , "optimally arranged" , "smarter than anything" , "Extremely organised" , "One orderly more than others" .)