Troop learns to avoid the regular drinkers (6)
I believe the answer is:
topers
'drinkers' is the definition.
(I know this)
'troop learns to avoid the regular' is the wordplay.
'to avoid the regular' means one should take alternating letters (letters removed at regular intervals).
'troop'+'learns'='trooplearns'
The alternating letters of 'trooplearns' are 'TOPERS'.
(Other definitions for topers that I've seen before include "Heavy drinkers" , "We regularly knock it back" , "Habitual imbibers" .)