As a wedding guest, you have to follow these simple social media rules:
Keep it to yourself: If the couple has not yet announced their engagement or wedding plans on their social media networks, don’t congratulate them online. Wait until the couple is ready to share the news themselves. Send a private message, call them or congratulate them in person.
Sharing the bride and groom’s pictures: Always ask the couple if they are OK with your sharing their pictures. Some will mind while others won’t, so just make sure you respect their wishes.
Don’t share your wedding planning questions: Yes the bride is your best friend but send any wedding related questions in a private message. The couple may have friends on their "friend" list who are not invited to the wedding and that will make it more awkward for them.