Wedding photography tips?

I'm taking pictures for my brothers wedding this Friday. He didn't give me anytime to prepare. I'm not a professional. I do want to be a professional photographer though. I'm nerves. Does anyone have any tips. I have a Nikon D3000 camera. I haven't seen the place they are getting married and I still don't know where it is until Friday. Any advice is welcomed.

Relax. No pressure. I'm sure he's not expecting you do take amazing pictures and youre probably doing it for free. Just relax and use this as a time to practice. But try to get a few great pics just for him.
Also you could use this to help get your portfolio up

Your best bet would be to visit the wedding site and experiment with different shots and angles from various positions. Ask what time of day the wedding will take place, where everything will be set, and take some shots to determine your best "shooting area".

First make sure your brother, and very importantly his bride, understand that you are unlikely to deliver fantastic wedding coverage and they may be disappointed. You may be a good photographer of landscapes or kids playing in the park, but wedding photography is demanding and takes some practice to get it right on top of having basic skill. So make sure they are prepared for whatever outcome they end up with, whether great or mediocre. Then sit them both down and ask them what shots they feel they must have. There are all sorts of lists on the bridal sites, print off one and go over it.

You'll almost certainly need a flash. Although you won't use it during the vows, you'll need it for the processional, recessional and reception. Get a dedicated Nikon flash (you can rent one if you're in a sizable city, or look on-line) and use it on auto-TTL. A diffuser would be nice, or bounce when you can.

Unless you are very very accustomed to shooting on manual, use program and adjust using exposure compensation when needed. Use a higher ISO when needed. Noise can be dealt with in post processing, but blur is forever. So watch your shutter speed and keep it at handholding numbers. You can use a tripod for the ceremony part and time shots carefully. Be sure to attend the rehearsal if they have one. Also talk to the officiant to see what is allowed concerning flash use and where you may be during the ceremony. Scout the location for possible formal portraits. If you can do them outside it would be a good idea to do so in addition to the ones at the altar or inside the venue.

Don't get fancy. Now is not the time to try new techniques or attempt to be artsy. Keep it simple. Look at some professional wedding sites (not FB) and pay attention to how the groups and couples are posed. Practice posing people. If you will do formal group shots of the wedding party and family, take control to make sure everyone is looking at you and not Aunt Edna on the side. Ask other snappers to let you get your shot first and get the subjects' attention on you before you shoot. Take several of each pose unless you are good at transposing eyes in post. Don't forget the detail shots of the decor, rings, cake, toasting glasses etc.

You also need a backup camera of some sort. Another dSLR would be better, but if not available at least have a P&S on hand. Don't forget extra memory and fully charged batteries. Eat beforehand and stay hydrated. Wear comfortable and quiet shoes. You will be working, so don't get lost in visiting with the family. You're in charge of capturing their special day and are no longer a guest. In a way, it is an unfair position your brother has put you in, but that is between y'all. I actually prefer to be the one behind the lens in family events myself. YMMV.

Finally here is a good link for first timers:

http://www.rokkorfiles.com/Wedding101-page1.html

Good luck, hope the day goes great and everyone is pleased in the end.