Be shrewd at work, noting who is organised (4,1,5,2,3)
I believe the answer is:
know a thing or two
'be shrewd' is the definition.
'at work noting who is organised' is the wordplay.
'is organised' indicates an anagram.
'at'+'work'+'noting'+'who'='atworknotingwho'
'atworknotingwho' anagrammed gives 'KNOW A THING OR TWO'.
(Other definitions for know a thing or two that I've seen before include "exceptionally ignorant?" , "Be astute" , "wise folk do" .)