Smartest visitor at table conks out coming in (7)
I believe the answer is:
tidiest
'smartest' is the definition.
('tidy' can be similar in meaning to 'smart')
'conks out coming in' is the wordplay.
'conks out' becomes 'dies' ('die' can be a synonym of 'conk out').
'coming' becomes 'tit' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'dies' going within 'tit' is 'TIDIEST'.
'visitor at table' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for tidiest that I've seen before include "most trim" , "smarter than anything" , "One orderly more than others" , "Neatest" , "optimally arranged" .)