The way to start work on a house (3)
I believe the answer is:
how
'the way' is the definition.
'start work on a house' is the wordplay.
'start' suggests taking the first letters.
'on' says to put letters next to each other.
'a house' becomes 'ho' (abbreviation for house).
The first letter of 'work' is 'w'.
'w' put after 'ho' is 'HOW'.
'to' acts as a link.
(Other definitions for how that I've seen before include "In what manner or method?" , "See 16" , "In what way?" , "By what means?" , "Who (anag.)" .)