Foremost in performance, tidy bit of acting (5)
I believe the answer is:
prima
'acting' is the definition.
Both the answer and definition are adjectives. Perhaps there's a link between them I don't understand?
'foremost in performance tidy bit' is the wordplay.
'foremost in' indicates taking the first letters.
'tidy bit' becomes 'rima' (I can't explain this - if you can you should give a lot more credence to this answer).
The first letter of 'performance' is 'p'.
'p'+'rima'='PRIMA'
'of' is the link.
Can you help me to learn more?
(Other definitions for prima that I've seen before include "in pole position" , "Top diva is a . . . . . donna" , "Leading" , "First" .)