Equipment wise a fast 17-70 and a fast zoom such as 70-200 (F2.8) it may be worth considering hiring the lenses if you don't own them.
I thought I would share a few of things I have learnt, if it is a church wedding try and get in contact with the vicar doing the wedding he will give a heads up on what is allowed and what isn't. Some of them won't allow photos at all during the main ceremony but will stage them afterwards.
Have a shooting plan which you discuss with the bride and groom, also think of some creative ideas yourself but priority on the day is make sure you bag the shots they want before you get creative.
Depending on what time of day it is watch your shutter speed, I shot a wedding in November which finished at 4:00 PM the light dropped rapidly and so did my shutter speed which can cause blurred shots.
If you use Auto at the moment get used to Aperture Priority mode I pretty much shot a whole wedding in this mode with exposure compensation, I did also use manual in the evening recepition.
When doing group photos fire off a few shots the bigger the group the more chance someone will be blinking, yawning, looking the wrong way etc. Talk and joke to the group it gets them looking your way and a joke causes smiles etc.
Try and do a practice shoot with the bride and groom prior to the event to get them comfortable with being photographed and teach them how to stand and pose.
As someone has already mentioned do a reccy of the venues, both reception and where the marriage happens.
Double check the night before you have memory cards, batteries, lenses, camera etc and also have a backup camera available even if it is a compact. Also check you camera settings i.e. not set at a high ISO etc
Try and get someone to assist with rounding up everyone for shots etc.
Check your histogram after shots and shoot in RAW or RAW+JPG as you can recover more detail in this mode.
As someone mentioned it is quite stressful but it is also great experience.
You may want to read a book on the subject
this in my opinion is excellent and covers all I have mentioned plus more.
I am not trying to frighten you BTW if you go in with your eyes open it is a lot easier on the day
