Listen to Doctor Rees! About practice! (8)
I believe the answer is:
rehearse
'practice' is the definition.
(I know that practice can be written as rehearse)
'listen to doctor rees about' is the wordplay.
'listen to' becomes 'hear' (to hear something is to listen to it).
'doctor' indicates anagramming the letters.
'about' indicates putting letters inside.
'rees' with letters rearranged gives 'rese'.
'hear' placed into 'rese' is 'REHEARSE'.
(Other definitions for rehearse that I've seen before include "What actor does to prepare for play" , "Practise parts" , "Cast practise for play" , "Practise like actor" , "Train" .)