Tuneful Spice Girl tackling loud bit now and then (7)
I believe the answer is:
melodic
'tuneful' is the definition.
(I've seen this in another clue)
'spice girl tackling loud bit now and then' is the wordplay.
'spice girl' becomes 'Mel C' (member of the Spice Girls).
'tackling' is an insertion indicator (to tackle is to take possession of).
'now and then' means one should take alternating letters (letters taken on a regular basis, now and then).
'loud'+'bit'='loudbit'
The alternating letters of 'loudbit' are 'odi'.
'melc' enclosing 'odi' is 'MELODIC'.
(Other definitions for melodic that I've seen before include "Old mice (anag.)" , "Pleasant-sound" , "Harmonious" , "nice on the ear" , "Of music, tuneful and sweet" .)