Rubbish! Best to leave quietly and say nothing (4)
I believe the answer is:
tosh
'rubbish' is the definition.
(I've seen this before)
'best to leave quietly and say nothing' is the wordplay.
'best' becomes 'top' ('top' can be similar in meaning to 'best').
'to leave' suggests deleting specific letters.
'quietly' becomes 'p' (p for piano and quiet).
'and' says to put letters next to each other.
'say nothing' becomes 'sh' (I've seen this in other clues).
'top' with 'p' taken out is 'to'.
'to'+'sh'='TOSH'
(Other definitions for tosh that I've seen before include "Rubbish; shot (anagram)" , "Slang nonsense" , "Stuff and nonsense" , "Cobblers" , "13 [TRIPE]" .)