Small company about to be successful (5)
I believe the answer is:
score
'be successful' is the definition.
(as in scoring a victory)
'small company about' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'company' becomes 'co' (abbreviation).
'about' becomes 're' (common abbreviation for 'with reference to').
's'+'co'+'re'='SCORE'
'to' acts as a link.
(Other definitions for score that I've seen before include "Shoot a goal for a twenty" , "Result" , "Tally; group of twenty" , "Tally in a game" , "Put ball in the net" .)