Overlook Holmfirth occasionally (4)
I believe the answer is:
omit
'overlook' is the definition.
(I know that overlook can be written as omit)
'holmfirth occasionally' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
The alternate letters of 'holmfirth' are 'OMIT'.
(Other definitions for omit that I've seen before include "Miss out" , "Fail to mention" , "Leave out or overlook" , "Leave something out" , "by-pass" .)