Important to prepare at first main tent (3,3)

I believe the answer is:

big top

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'main tent' is the definition.
'big top' can be an answer for 'tent' (big top is a kind of tent). I am unsure of the 'main' bit.

'important to prepare at first' is the wordplay.
'important' becomes 'big' (synonyms).
'at first' indicates taking the first letters.
The first letter of 'prepare' is 'p'.
'big'+'to'+'p'='BIG TOP'

Can you help me to learn more?

(Other definitions for big top that I've seen before include "needed by Mae West, for one?" , "Circus venue" , "'Main circus tent (3,3)'" , "entertainment centre" , "performance in The Ring" .)

I've seen this clue in The Sun.

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