Go quietly when external trade is bad (6)
I believe the answer is:
depart
'go quietly' is the definition.
'depart' can be an answer for 'go' (synonyms). I'm not sure about the 'quietly' bit.
'when external trade is bad' is the wordplay.
'when' becomes 'p' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'external' means one lot of letters goes inside another (I've seen this in other clues).
'is bad' indicates anagramming the letters (I've seen 'being bad' mean this).
'trade' anagrammed gives 'deart'.
'p' placed inside 'deart' is 'DEPART'.
Can you help me to learn more?
(Other definitions for depart that I've seen before include "Stray" , "Leave (6)" , "make tracks" , "Clearly expressive" , "Start out" .)