Preparing non-universal leaf mould, squeeze once (3,5)
I believe the answer is:
old flame
'squeeze once' is the definition.
(squeeze can mean a lover or romantic partner)
'preparing non-universal leaf mould' is the wordplay.
'preparing' indicates an anagram (the same letters prepared differently).
'non' suggests deleting specific letters.
'universal' becomes 'U' (film certificate).
'leaf'+'mould'='leafmould'
'leafmould' with 'u' removed is 'leafmold'.
'leafmold' anagrammed gives 'OLD FLAME'.
(Other definitions for old flame that I've seen before include "Former lover" , "Former partner" , "Someone once loved" , "still 1 across [ALIGHT], it seems" , "Ex" .)