Best party, getting gone in the head! (5)
I believe the answer is:
outdo
'best' is the definition.
(synonyms)
'party getting gone in the head' is the wordplay.
'party' becomes 'do' (do can informally mean a party).
'getting' means one lot of letters go next to another.
'gone in' becomes 'ou' (I can't explain this - if you can you should give a lot more credence to this answer).
'head' says to take the initial letters.
The first letter of 'the' is 't'.
'ou'+'t'='out'
'do' put after 'out' is 'OUTDO'.
Can you help me to learn more?
(Other definitions for outdo that I've seen before include "Surpass, go one better than" , "Get the better of" , "Surpass - overshadow - excel" , "Br superior to (someone)" , "Surpass someone at something" .)