I probably could have titled this blog post a thousand different things from "Things to tell your wedding guests before your wedding day" to "How to make your wedding photographer's life easier" or simply "How to make sure you get the best possible wedding photos".
It's actually quite simple. You just need to make your guests aware of a few things.
1. Don't stand in the way of the official wedding photographer. I get it you want some snaps of your niece/best friend/brother/partner-in-crime's big day for your own album or just to share some images from your perspective and that's great. Go for it, but please make sure to not stand in the way of the professional photographer, hindering them doing their job to their best of abilities. It'd be annoying for the happy couple to have the photos of their first official kiss as husband and wife destroyed by a mobile phone distracting the view. There are so many moments during a wedding that can't be repeated and are over in a few seconds.
2. If you want to take photos on your phone or camera PLEASE turn off the flash. Why? Same reason as the first point. 99% of the time a flash (that's not the wedding photographer's) going off can distract the image or even ruin their shot and they may only get one chance to capture that special moment.
3. Don't distract the people having group shots taken. Depending on the size of the wedding party it can take some time to get the crowd's attention and organise a big group of people to get everyone in the shot. I always ask everyone to look at the camera (repeatedly), but it's natural to look at familiar faces holding a phone or camera up to take some photos as well. Feel free to take some pictures, but please wait until the photographer is done, so that everyone is looking where they're supposed to for the official photos.
4. Enjoy yourself and don't worry so much about the photographer. There's no need to stop your conversation to pose for photos - carry on, it's all about the candid shots. Of course it's fine to take some posed shot's with someone, but from experience the most loved/most memorable images are the real and candid ones.
There are different ways to let your guest know about the above points/rules and it's obviously up to you, some clients have a wedding website or a wedding magazine for their big day where they make everyone aware or they publish out a FB post or send an email to everyone, just to name a few, but I can promise you doing so will make all the difference and your photographer will be grateful and appreciate your help!
Some couples decide to go for an "unplugged" wedding/ceremony, which will definitely help with the above listed issues and makes your big day so much more personal and special. If you need help with telling your guests about your unplugged wedding here's another link that I found quite helpful.
That said, you can get some fun images with mobile phones, especially during your reception or bridal/groom prep...