Guide one into bed! (5)
I believe the answer is:
pilot
'guide' is the definition.
(piloting is a kind of guiding)
'one into bed' is the wordplay.
'one' becomes 'i' (Roman numeral).
'into' means one lot of letters goes inside another.
'bed' becomes 'plot' (I've seen this before).
'i' inserted within 'plot' is 'PILOT'.
(Other definitions for pilot that I've seen before include "Flier or helmsman" , "Experimental scheme; flyer" , "Person in charge of aircraft" , "who shows the way?" , "Guide, steer" .)