Drool over books in sale now and then by monarch (7)
I believe the answer is:
slobber
'drool over' is the definition.
'slobber' can be an answer for 'drool' (I know this). I am not certain of the 'over' bit.
'books in sale now and then by monarch' is the wordplay.
'books' becomes 'bb' (two abbreviations for book).
'in' indicates putting letters inside.
'now and then' means one should take alternating letters (letters taken on a regular basis, now and then).
'by monarch' becomes 'oer' (I can't justify this - if you can you should give a lot more credence to this answer).
The alternating letters of 'sale' are 'sl'.
'sl'+'oer'='sloer'
'bb' going inside 'sloer' is 'SLOBBER'.
Can you help me to learn more?
(Other definitions for slobber that I've seen before include "Salivate excessively" , "maudlin behaviour" , "Drip saliva" , "Drool disgustingly" , "Behave with excessive affection, dribble" .)