Beer gets no better on one’s own (5)
I believe the answer is:
alone
'on one's own' is the definition.
(I've seen this before)
'beer gets no better' is the wordplay.
'beer' becomes 'ale' (type of beer).
'gets' indicates putting letters inside (gets can mean captures or absorbs).
'better' indicates anagramming the letters (with an improved letter-order).
'no' with letters rearranged gives 'on'.
'ale' going around 'on' is 'ALONE'.
(Other definitions for alone that I've seen before include "Without anybody or anything else" , "without another" , "Isolated; exclusively" , "Exclusively, by oneself" , "Unaccompanied" .)