The best clue to first of puzzles
I believe the answer is:
tiptop
'the best' is the definition.
(thesaurus)
'clue to first of puzzles' is the wordplay.
'clue' becomes 'tip' (I've seen this before).
'first of puzzles' becomes 'p' (1st letter of 'puzzles').
'tip'+'to'+'p'='TIPTOP'
(Other definitions for tiptop that I've seen before include "The height of excellence" , "Excellent, super" , "The pinnacle of perfection" , "Best of its kind" , "Informally excellent, very best" .)