About to have a party, tax yourself unduly (6)
I believe the answer is:
overdo
'tax yourself unduly' is the definition.
I can't judge whether this definition defines the answer.
'about to have a party' is the wordplay.
'about' becomes 'over' (both can mean around).
'to have' means one lot of letters go next to another.
'a party' becomes 'do' (do can informally mean a party).
'over'+'do'='OVERDO'
Can you help me to learn more?
(Other definitions for overdo that I've seen before include "Cook wrongly" , "Sum of a persons actions (Hinduism)" , "Use to excess" , "Carry to excess" , "Work too much" .)