Parking on new street -- it's becoming most attractive (9)
I believe the answer is:
prettiest
'most attractive' is the definition.
(I've seen this before)
'parking on new street it's' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'new' is an anagram indicator.
'street'+'it'='streetit'
'streetit' is an anagram of 'rettiest'.
'p'+'rettiest'='PRETTIEST'
'becoming' is the link.
(Other definitions for prettiest that I've seen before include "Most charming" , "Most attractive" , "Most beautiful" .)