Make a mountain out of a molehill, for instance — I tear into all (anag) (12)
I believe the answer is:
alliteration
(Other definitions for alliteration that I've seen before include "Peter practised poetic ploy perfectly" , "Successive starts sounding similarly" , "Poetic rhyming device using words with the same initial letter" , "Repeated first letters" , "Poetic ploy practised with panache!" .)