Tidier new diner? (6)
I believe the answer is:
neater
'tidier' is the definition.
('neat' can be similar in meaning to 'tidy')
'new diner?' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'diner?' becomes 'eater' (to dine is to eat a meal).
'n'+'eater'='NEATER'
(Other definitions for neater that I've seen before include "straighter" , "Better" , "approaching apple-pie order" , "More tidy and orderly" , "Tidier" .)