I voted and got it right
When I was asked to do my first wedding I refused. They asked again and I refused again. Then they asked a third time
So, I went on a workshop and, okay I did learn a few bits and pieces but not much to be honest - YouTube is what saved me. I watched probably a week's worth of videos over the next few months.
Based on what I knew for my first one I'll offer this - it's not necessarily advice but more how I felt at that time and how I tackled it. Feel free to take it or leave it. In reverse order of priority:
4. This is a brilliant video - no camera involved either! And once watched and notes taken, have an engagement shoot practice with the couple so you can get used to them, have some practice with them and let them get used to you. And remember to talk to them during the practice. This is important as the easiest thing to do is clam up and concentrate on your photos and then they start wondering what to do and go silent and then you get a bit stuck and it becomes worse and then you freeze ... you need to talk to them then they respond and it's so much easier, and much more relaxing.
And at the wedding just try and remember a few bits from the engagement shoot that you learned and the video to try and improve some of the shots. It's not a modelling session; it's a wedding and the couple will be more interested in having a grand time than having their photos taken. The video is for your benefit just to watch for some of the details you can correct and how to improve the posing.
3. Exposure - you don't want to over expose the bride's dress and fill in flash can work wonders on faces. If you know what you're doing that's great but if you don't find someone to give you a lesson or two with this and/or watch a few YouTube videos - some are good but some aren't. And can you practice on your wife/partner wearing white clothing? A battery grip isn't essential but a flash gun is.
2. Take note of most/all of the above posts (and, presumably, posts following after this one) - there is some really helpful information on this forum.
1. Most important - ENJOY yourself!! This takes pressure off you and you relax and smile and talk, which makes others smile more and they feel more comfortable and chat to you which makes you feel more comfortable. And then the photos happen much more naturally. And some people just like to show off in front of a camera so you just click away!
And re the battery grip - I did buy one but hardly ever use it as it goes through batteries much more quickly than the single one in the camera.
Best of luck!!