VIP's black rug holds soldier up (6)
I believe the answer is:
bigwig
'vip's' is the definition.
(I've seen this in another clue)
'black rug holds soldier up' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'rug' becomes 'wig' ('rug' is an informal term for a wig).
'holds' means one lot of letters goes inside another.
'soldier' becomes 'GI' (GI can mean a US soldier).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'gi' back-to-front is 'ig'.
'b'+'wig'='bwig'
'bwig' placed around 'ig' is 'BIGWIG'.
(Other definitions for bigwig that I've seen before include "Important person (slang)" , "important figure" , "Personage" , "'Chief, top banana (6)'" , "Mogul" .)