One should be in entering a new trade (7)
I believe the answer is:
trained
'one' is the definition.
Both the answer and definition are adjectives. Perhaps there's a link between them I don't understand?
'in entering a new trade' is the wordplay.
'entering' means one lot of letters goes inside another.
'a new' indicates anagramming the letters.
'trade' is an anagram of 'traed'.
'in' put within 'traed' is 'TRAINED'.
'should be' acts as a link.
Can you help me to learn more?
(Other definitions for trained that I've seen before include "I daren't (anag)" , "Taught (a skill)" , "Taught (to do a job)" , "Taught; exercised" , "Prepared for a task or career" .)