Some other things to keep in mind regarding taking photos at weddings are:
Stay in the moment as a guest. So many people are so busy taking pictures, texting and tweeting that they miss the firsthand experience of being there. Don't allow your phone to become your social crutch. It is OK to put it away for the duration. Send those texts and tweets after the reception.
Don't take flash photos during the ceremony, especially, if it is in a church. It takes away from the solemnity of the service and is very distracting to everyone else. Professional photographers are usually adept at staying inconspicuous while shooting in a church. However, some churches ask that no one, even the professionals, take photos during the ceremony.
Do ask a family friend who is good at taking photos to snap candid shots.
There are a lot of candid moments a professional photographer can't get due to time constraints. This is where someone shooting candid shots, especially if this person knows many of the guests and their relationship to the bride and groom, can get some great shots. However, it is important for them to stay out of the way of the professionals.
Get permission from the bride and groom, or their family, before sharing your photos on social media. You don't want to steal their thunder. Remember, it is their day, not yours. Professional photographers should get permission before posting photos on their websites, too.