Try slack regional centre penning ticket (4,2,1,2)
I believe the answer is:
give it a go
'try' is the definition.
(I've seen this before)
'slack regional centre penning ticket' is the wordplay.
'slack' becomes 'give' (I've seen this in another clue).
'centre' indicates the central letters.
'penning' is an insertion indicator.
'ticket' becomes 'tag' (I've seen this in another clue).
The central letters of 'regional' are 'io'.
'io' going around 'tag' is 'itago'.
'give'+'itago'='GIVE IT A GO'
(Other definitions for give it a go that I've seen before include "Try" , "Have a shot at, make an attempt" , "Make an attempt at something" .)