Do this, and museum lies in ruins? (9)
I believe the answer is:
vandalise
'do' is the definition.
Although both the answer and definition are verbs in their base form, I don't see how they can define each other.
'and museum lies in ruins?' is the wordplay.
I cannot quite see how this works, but
an anagram of 'and' is 'nda' which is located in the answer.
'museum' could be 'va' (Victoria and Albert Museum, or 'V and A') and 'va' is found within the answer.
an anagram of 'lies' is 'lise' which is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'this' acts as a link.
Can you help me to learn more?
(Other definitions for vandalise that I've seen before include "Wreck" , "Wilfully damage" , "Destroy" , "trash" , "Inflict malicious damage" .)