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' means one lot of letters goes inside another.
The final letter of 'you' is 'u'.
'u' put into '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" .)