Do first things first (5)

I believe the answer is:

start

'first' is the definition.
(I know that first can be written as start)

'do first things' is the wordplay.
'do' becomes 'star' (starring is a kind of doing).
'first things' becomes 't' (sst letter of 'things').
'star'+'t'='START'

(Other definitions for start that I've seen before include "Begin - jump" , "Jerk" , "open" , "Move quickly < when surprised" , "Beginning" .)

I've seen this clue in the Evening Standard.

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