I had been first but didn't work (5)
I believe the answer is:
idled
'but didn't work' is the definition.
I can't tell whether this defines the answer.
'i had been' is the wordplay.
'i had' becomes 'i'd' (I'd).
'been' becomes 'led' (leading is a kind of being).
'id'+'led'='IDLED'
'first' acts as a link.
Can you help me to learn more?
(Other definitions for idled that I've seen before include "pottered" , "Of engine, just ticked over" , "Turned over" , "sat back" , "Was lazy" .)