The Right Camera
The first place to start is a high quality, state of the art camera. These can be pricey, so if you don't already have one, see if a friend will loan you hers. You will want a digital camera so that you can transfer the data onto a CD and easily make production copies later. These also usually offer editing features which will come in handy when you are finalizing your video.
A good video camera has a video finder that offers a clear view of what you're shooting. Many digital cameras have a small screen to the side of the viewfinder so that you can see how the material will look once it is viewed by the recipient.
Try out a few different features on your camera before the big day. Zoom, fade, grain and other actions can all add nice touches to the final tape.
Watch Your Lighting
Be sure your camera is set to accommodate the lighting. You don't want material that is too dark to see later on, or so bright that the bride and groom's faces are lost in the shine. Find out where the wedding will be taking place and see if the manager (or the church or synagogue) will allow you to do a few test shots in advance. Try several different lighting schemes, then go home and view them to find out which works best.
Have Backup
If you're nervous about losing material, not catching the best shots or simply hitting the wrong button at the wrong time, see if a trusted friend can stand nearby to shoot a second tape simultaneously. This can offer peace of mind and will make it easier later on to select the best possible footage.
Where to Stand
Be as unobtrusive as possible, but do find a good position in which to film your footage. Standing off to the side at an angle that accommodates the bride and groom's faces clearly is best. Here is where your zoom feature will really come in handy; you don't want to be a distraction, but you will want to catch the sentimental details on film.
Extra Help
Consider a wedding video production workshop. One may be being held in your area at some time before the wedding. Search online for listings of wedding shows that may offer this service. The money you spend on the seminar will be worth its weight in gold later on.
Making a Scrapbook
In addition to the full-length feature, you can also make a wedding scrapbook out of still shots captured from the tape. This makes a lovely gift for the bride and groom.
Public Showing
You (or the happy couple) can share the happy moments by uploading highlights onto your computer and finding an online photo album service. These are often free and can be great for people who were unable to attend but would have liked to share your special day.
Remember: you're making memories. It is better to shoot too much footage than too little. Have fun with this, and be creative for a wedding video tape you'll want to watch over and over again.