What sort of time? If it's after 10pm head to Lakota or Clockwork if there is a decent night on, but there are a lot of good pubs also. The Croft to a decent drop of cider, but if you heard further up there are more pubs... Keep your wits about you, as there has been there was shooting outside club UK a while back, but this was related to Yardie gangs, so as long as there is not a dancehall night on you should be ok!
EDIT: I misread the title, I thought you put "Gloucester Road, Bristol", if you cover the whole of Bristol then there are a few nicer areas, what sort of thing are you after?