Make an effort on tune (6)
I believe the answer is:
strain
I believe this clue is a double definition.
'make an effort' is the first definition.
(I've seen this before)
'tune' is the second definition.
(I've seen this before)
'on' is the link.
(Other definitions for strain that I've seen before include "Family - tension" , "Tension - stock" , "Distinct breed; use a seive" , "Sieve; breed" , "Exert oneself to the utmost" .)