At home, instruct one fellow to be smart (11)
I believe the answer is:
intelligent
'be smart' is the definition.
('intelligent' can be similar in meaning to 'smart')
'at home instruct one fellow' is the wordplay.
'at home' becomes 'in' ('in' can be similar in meaning to 'at home').
'instruct' becomes 'tell' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'fellow' becomes 'gent' (I've seen this before**).
'in'+'tell'+'i'+'gent'='INTELLIGENT'
'to' is the link.
(Other definitions for intelligent that I've seen before include "7 [CLEVER]" , "Smart" , "displaying brainpower" , "Bright, quick of mind" , "Able to reason; well-informed" .)