Straighten up exterior of Queen's London address (6)
I believe the answer is:
strand
'straighten' is the definition.
Although both the answer and definition are verbs in their base form, I can't understand how they can define each other.
'up exterior of queen's london address' is the wordplay.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'exterior of' says to hollow out the word (remove centre letters).
'queen's' becomes 'Titania's' (fairy queen).
'london address' becomes 'rand' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'titanias' with its centre removed is 'ts'.
'ts' back-to-front is 'st'.
'st'+'rand'='STRAND'
Can you help me to learn more?
(Other definitions for strand that I've seen before include "A thread or a sea shore" , "Run aground, beach" , "string" , "Drive aground on shore" , "Ply" .)