Firstly you should think about what style of wedding photography appeals to you. Bookmark some of your favourite wedding photography sites or browse some wedding photography blogs to get an idea of the style that appeals to you most. Do you like the natural photojournalistic style, the more traditional posed images or a combination of the above. This combination seems to be the most popular style of wedding photographer at the moment as it gives couples the best of both worlds. Documentary wedding photography that tells the story of the day from bridal preparation shots all the way through to the end of the day as well as some posed photographs that will guarantee you some nice pictures to frame.
f you're not a fan of old fashioned posed shots then getting a great photographer is even more critical. A great wedding photographer should be an expert in staging situations to make them look as un-posed as possible. This is far more difficult than getting a couple to just stand there and smile but the results can be amazing. Make sure that the photographers that you narrow down can capture the type of photographs that you're after.
Secondly, you should make sure you're looking at ‘real' wedding photography images. It's easy to get drawn in to website portfolio images of amazing looking brides on a photographers homepage that have been captured in a studio or as part of a photoshoot. Many wedding photographers will attend special courses or portfolio building sessions that allow them to photograph model brides with studio lighting to help strengthen their portfolio. Real weddings are completely different and you should make sure that the photographs you're looking at were taken as part of a real wedding.
Lastly, you should go with what you like, not what you're told. Although recommendations from friends are good, it doesn't mean that the wedding photographer that they picked is right for you. Not all photographers have the same style so you should make sure that you get someone who photographs the style that you want and not try to get someone with a different style to try and adapt to what you want.