I would start entertaining a friend in the best possible way (7)
I believe the answer is:
ideally
'in the best possible way' is the definition.
(I've seen this before)
'i would start entertaining a friend' is the wordplay.
'i would' becomes 'I'd'.
'start' suggests taking the first letters.
'a friend' becomes 'ally' (synonyms).
The initial letter of 'entertaining' is 'e'.
'id'+'e'+'ally'='IDEALLY'
(Other definitions for ideally that I've seen before include "for best results" , "In a perfect world, the best possible situation" , "for preference" , "Perfectly; most suitably" , "In the best possible scenario" .)