Drill for dubious race tips (8)
I believe the answer is:
practise
'drill' is the definition.
('practise' can be a synonym of 'drill')
'dubious race tips' is the wordplay.
'dubious' is an anagram indicator.
'race'+'tips'='racetips'
'racetips' is an anagram of 'PRACTISE'.
'for' acts as a link.
(Other definitions for practise that I've seen before include "Rehearse" , "Do something to improve skill, train" , "Custom" , "Train by repetition" , "Be engaged in (profession)" .)