Prepare to shoot first-rate male (3)
I believe the answer is:
aim
'prepare to shoot' is the definition.
(as in aiming a gun)
'first-rate male' is the wordplay.
'first rate' becomes 'AI' (resembles A1, old-fashioned slang for very good).
'male' becomes 'm' (common abbreviation).
'ai'+'m'='AIM'
(Other definitions for aim that I've seen before include "Aspire" , "Direct; intention" , "intent" , "Attempt" , "Point (a camera)" .)