Patron reveals routine followed by old queen (8)
I believe the answer is:
customer
'patron' is the definition.
(I've seen this before)
'routine followed by old queen' is the wordplay.
I cannot really understand how this works, but
'old' could be 'o' (abbreviation) and 'o' is found within the answer.
'queen' could be 'er' (short for Elizabeth Regina ie Queen Elizabeth) and 'er' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'reveals' acts as a link.
Can you help me to learn more?
(Other definitions for customer that I've seen before include "Shopper or client - always right" , "Someone shopping" , "The one who pays is always right" , "Someone who pays for goods or services" , "The person who is said in business to be always right" .)