Argueabley the most anticipated moment of the wedding, the marriage service!
This is the part of the day where I have to be the most "discreet" I can be, trying to capture the key moments of the service without disturbing anything or anyone!
Some ceremonies are easier to shoot than others. The first thing I observe is the light. You really can't control this, but you can approach it differently if you have time to look around!
After looking at the lighting situation, I then try to establish a good relationship with the service conductor, whether that be a registrar or vicar/priest. Some conductors are more lenient than others when working with photographers. Some wish for you to stand in a certain position throughout the service, whilst others allow you to move freely to get the best shot, with the trust that the photographer won't interrupt or disturb the service. I'd say most civil ceremonies have a more laid back approach when working with photographers, but it tends to be a bit more inconsistent when working in religious premises.
My approach to a wedding day is simple, to capture it as naturally and authentically as possible, so I'm always careful to hang fire when capturing key moments!