The luck of the Irish cueists every now and again (4)
I believe the answer is:
cess
'the luck of the irish' is the definition.
(Irish word meaning luck or fortune)
'cueists every now and again' is the wordplay.
'every now and again' means one should take alternating letters.
The alternate letters of 'cueists' are 'CESS'.
(Other definitions for cess that I've seen before include "Tax, levy (Sc., Ir.)" , "Old local rate" , "Tax old" .)