Start as you finish, in debt! (5)
I believe the answer is:
debut
'start' is the definition.
(debut is a kind of start)
'you finish in debt' is the wordplay.
'finish' indicates one should take the final letters.
'in' indicates putting letters inside.
The final letter of 'you' is 'u'.
'u' going within 'debt' is 'DEBUT'.
'as' acts as a link.
(Other definitions for debut that I've seen before include "Tubed (anag.)" , "Appear in public for the first time" , "The coming out of a society girl" , "First appearance, coming out" , "First appearance in society" .)