Shake Mel and Bert? Rubbish! (7)
I believe the answer is:
tremble
'shake' is the definition.
(I know that shake can be written as tremble)
'mel and bert? rubbish' is the wordplay.
'and' says to put letters next to each other.
'rubbish' indicates anagramming the letters (a poor quality or rubbish spelling of the letters).
'mel' after 'bert' is 'bertmel'.
'bertmel' anagrammed gives 'TREMBLE'.
(Other definitions for tremble that I've seen before include "Shake with fright or cold" , "Shake with fear or excitement" , "sign of nerves" , "Quake in one's shoes" , "Quakers do this" .)