Look around for one constructive thing to do (4)
I believe the answer is:
lego
'constructive thing to do' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'look around for one' is the wordplay.
'look' becomes 'lo' (archaic exclamation meaning 'look!').
'around' means one lot of letters goes inside another.
'for one' becomes 'eg' (both can mean 'for example').
'lo' placed around 'eg' is 'LEGO'.
Can you help me to learn more?
(Other definitions for lego that I've seen before include "Toy construction set" , "Building bricks for children" , "Toy building-bricks" , "Toy with interlocking blocks" , "Child's building bricks" .)