The most effective approach is to include a clear, specific request in your wedding invitations or a note sent beforehand - something like "We'd love to keep phones away during the ceremony so we can all be fully present, and we're asking guests not to share photos on social media until after we've released our official ones." The key thing people miss is that a verbal request alone often gets forgotten in the moment, especially by the relatives most prone to oversharing, so having it in writing makes it feel less like a personal judgment and more like a standard part of your wedding logistics. You could also designate one trusted person to gently remind guests as they arrive, framing it as a photography thing rather than a privacy thing - that tends to land better than emphasizing your discomfort with their behavior.