Pop singer, mostly with guitarist Paul after good laughs (7)
I believe the answer is:
giggles
'laughs' is the definition.
(giggle is a kind of laugh)
'pop singer mostly with guitarist paul after good' is the wordplay.
'pop singer mostly' becomes 'gig' (I can't justify this - if you can you should give a lot more credence to this answer).
'with' says to put letters next to each other.
'guitarist paul' becomes 'les' (Les Paul).
'after' says to put letters next to each other.
'good' becomes 'g' (abbreviation).
'les' after 'g' is 'gles'.
'gig' next to 'gles' is 'GIGGLES'.
(Other definitions for giggles that I've seen before include "Nervous laughs" , "Uncontrollable laughter" , "Titters" , "Has a chuckle" .)