Artist may work at this line, simplicity coming first (5)
I believe the answer is:
easel
'artist may work at this' is the definition.
(an artist might use an easel)
'line simplicity coming first' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'simplicity' becomes 'ease' (synonyms).
'coming first' is a charade indicator (letters next to each other).
'l' after 'ease' is 'EASEL'.
(Other definitions for easel that I've seen before include "supporter of board, perhaps" , "Lease out the stand" , "Artist's stand for painting" , "stand supporting artistic effort" , "Constable's stand?" .)