A lot of people, when looking for a good wedding photographer, will look for photographers that not only shoot great post photos but also shoot really great candid photographs. The first tip I would give you is be observant. Notice the subtle nuances, the relationship between the bride and the groom, and hone in on those moments and those nuances. Just look for things out of the ordinary. Get different angles. Get low. Get high.
Another really good way to get great candids is to just blend into the scene. Don't be obnoxious. Don't be up in people's space. Because if they see you you're not going to get a candid. It's going to be a forced, posed picture.
I spend a lot of time when shooting any event positioning myself as a fly on the wall just blending in and taking in the scene. I worked for a photographer for a while who said no matter what he's shooting the first thing he does is get a lay of the land. Again, what that means is just taking into account everything that's there including the relationships and nuances, and using that to his advantage as he shoots the event.
A lot of times, especially the weddings, it's easy to anticipate when the couple might kiss, they might hug, or they might dance. Look for special moments outside of the wedding, too. Maybe they're whispering in each other's ear at a table or something. If you're looking for something like that you can catch it from across the room and have them have no idea you even got it.
Another really great way to get good candids is to make sure that you're comfortable with the people you're photographing and they're comfortable with you. With a wedding especially you want to kind of develop a relationship before it. Get to know the people. Don't act like a business proprietor photographing a client. Make it that you're there because you want to be there and you want to get these great photographs. And make sure they know that. The more they know that the more comfortable they're going to be with you and the better photographs you'll get overall.