I've only shot one wedding in the past as a favour for my brother, and I'll admit, it was kind of tricky. Though I think that mainly came down to the situation I was in. I wouldn't advise being a guest at the wedding you're shooting - lots of aunts and uncles pulling you to the side telling you how much you've grown (Yes, I would have hoped I'd grown a bit over the past 20 years now please let me go and get a shot of the cake before they cut it).
Mine was very run and gun as it was a last minute thing. I had two cams for the ceremony but only one for the reception. Make sure you've got some stabilization you can move around quickly with as well (no-one likes jittery footage). Monopods are really great or a light tripod or some kind of steadicam if you've got it.
Your brothers friend will be well aware it's your first time shooting, and I'm guessing you're doing it for a significantly reduced rate so don't feel too pressured. Just keep calm, catch all the key moments, get lots of pretty B-roll, maybe even take the bride and groom aside for some real money shots and then you can really find and craft the story in the edit.
Oh - and get friendly with the photographer as well. If you get them onside you'll be able to work together finding decent shots and angles. Plus it's always nice to have someone to talk to.
I've been working as a freelance editor for a while now and pricing has always been frustrating. I know exactly how much I value my time and my service, but I agree with others in this post that in general, people are un-educated in the amount of skill, time and effort something will take - and sometimes - just want something for nothing.
I've been recently looking into going into production but I'm put off as I can see myself hitting the same pitfalls again, and losing moral.
SIDE RANT - I'm a video editor not a magician. If you over-expose your footage to the point that it looks like I'm staring up at the 'pearly-gates' or distort your audio so much it sounds like I'm listening to Slayer, there is very little I can do about that - SIDE RANT OVER.