After a poor start, a successful conclusion, mate! (3)
I believe the answer is:
pal
'mate' is the definition.
(both can mean a friend)
'after a poor start a successful conclusion' is the wordplay.
'after' is a charade indicator (letters next to each other).
'start' suggests taking the first letters.
'conclusion' says to take the final letters.
The first letter of 'poor' is 'p'.
The last letter of 'successful' is 'l'.
'p'+'a' is 'pa'.
'pa'+'l'='PAL'
(Other definitions for pal that I've seen before include "Brother" , "Mate, informal friend" , "China" , "Bud" , "Buddy, chum" .)