As with all people photography, the quality of images obtained is, at least to some extent, dependent upon the ease of the photographic relationship between photographer and subjects. A strained or tense relationship makes relaxed expressions more difficult to capture, so it is certainly worth the time and effort to at least break the ice.
There may be several opportunities to achieve a basic photographic relationship with the bride and groom, and perhaps some of the closer relatives. Make a point of meeting the couple before the wedding, at least when they live locally. The meeting might be to discuss their requirements or the detailed plans for the wedding day. A meeting can also be scheduled just to meet and get to know the bride and groom. Another opportunity presents itself when the couple want pre-wedding or engagement pictures, although it could equally be argued that such sessions should also be preceded by a get-to-know-you meeting.
The advantages of having developed a working relationship with the couple prior to the wedding should be immediately obvious. If the bride requires photographs of her private preparations on the day of the wedding, you should be greeted by smiles rather than formal introductions when you arrive at her home. She will already trust you and feel confident in your discretion and professionalism, so will have one thing less to worry about as she puts on her bridal gown.