Reviews from trusted, informed people (ie not imdb reviewers, or God forbid a glance a Rotten Tomatoes scores, or other ghastly, meaningless aggregators). By the way, a good reviewer doesn't necessarily mean someone with whom you always agree. Mark Kermode is my favourite living film critic (Barry Norman held that title before he died), but I have disagreed with him on a number of occasions. However, his opinion is informed, and that's an important difference.