Deceive girl mostly wanting heavy metal (7)
I believe the answer is:
mislead
'deceive' is the definition.
(I know that deceive is a more specific form of mislead)
'girl mostly wanting heavy metal' is the wordplay.
'girl mostly' becomes 'mis' (I can't explain this - if you can you should give a lot more credence to this answer).
'wanting' is a charade indicator (letters next to each other).
'heavy metal' becomes 'lead' (lead is a heavy metal).
'mis'+'lead'='MISLEAD'
Can you help me to learn more?
(Other definitions for mislead that I've seen before include "Give a wrong impression to (someone)" , "Take someone in the wrong direction" , "Hoodwink" , "Cause someone to believe something is not true" , "Cause someone to have a false belief" .)