Northerner first to sit on bed (4)
I believe the answer is:
scot
'northerner' is the definition.
(someone from Scotland)
'first to sit on bed' is the wordplay.
'first to' says to take the initial letters.
'on' is a charade indicator (letters next to each other).
'bed' becomes 'cot' (cot is a kind of bed).
The initial letter of 'sit' is 's'.
's'+'cot'='SCOT'
(Other definitions for scot that I've seen before include "one from the North of Britain" , "Highlander, for example" , "9 [KEIR HARDIE], say" , "Highlander perhaps" , "Jock?" .)