Finish first with the help of being sober (5)

I believe the answer is:

staid

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'sober' is the definition.
(synonyms)

'finish first with the help of' is the wordplay.
'finish' means to take half the letters.
'first' becomes 'erst' (I've seen this before).
'with the help of' becomes 'aid' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'erst' halved is 'st'.
'st'+'aid'='STAID'

'being' acts as a link.

Can you help me to learn more?

(Other definitions for staid that I've seen before include "Unadventurous, dull" , "Sober, grave" , "Calm, respectable and unadventurous" , "Settled" , "Sedate, decorous" .)

I've seen this clue in the Evening Standard.

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