For some beer styles, you can use classic beers as your standard of comparison to help educate your palate on what a particular beer style tastes like. For example, North Coast Old Rasputin is a good example of a Russian imperial stout, and Old Speckled Hen (Greene King Brewery) is a good example of an English pale ale.
In addition, always look for local and fresh examples and brewers and distributors who take good care of the beer.