My sister in law has asked me to photograph her wedding, and...

My sister in law has asked me to photograph her wedding, and this will be a first for me. I am doing it for free, and really want to do a good job. Its going to be a pretty laid back affair, and I will be using a canon T1I, with my 50mm lens. I have a supack pz42x flash, and am carrying with me 2 extra batteries nd 2 16 gb cards for backup. If there are any experienced wedding photographers here I would appreciate if you told me what the single most important thing about wedding photography is. Thanks.

Tough one. I don't think I can come up with one single most important thing, there are so many equally important things. So, for your first time:
1. Make a list (in order) of the shots you need to take, and what special (if any) shots the bride would like you to take. Things move fast and it's easy to miss something, so go by the list.
2. Be prepared to shoot at all times. Even if it's not on the list. If you think it would be a good shot, take it.
3. Don't be shy, but don't be rude. Get in there and shoot. It's what you are supposed to be doing.
If guests get in your way, move around them or ask them to move aside and let you get this shot.
4. Be on time. Be prepared. This is not the time to be fooling around with your equipment.
5. Take plenty of shots. It's better to have too many than not enough.
6. This may be the most important. I would not shoot a wedding with just one camera, lens and flash. I realize you are not a professional wedding photographer, but if something happens to your gear, you're done! Try to borrow a second camera setup if you can. Even a point and shoot can save the day.
7. Be sure you know how to operate your camera and if you borrow a second, be sure you know how to operate it.
8. Make sure your sister-in-law understands this is your first wedding shoot and although you may get professional results, you are not a seasoned pro (yet).
9. If you have a wide angle lens, bring it. You may find it very useful.
10. Don't use flash during the ceremony in the church unless you clear the use of flash first with the church.
11. Stay off the ALTER. Personally, I think it's rude.
12. A "flip flash bracket" is always useful.

These thoughts are just the tip of the iceberg. It would be easier if you had specific questions

Oh yea, take a look at "Planet Neil". He is a wedding photog. You may find his site interesting.

Good luck, have fun, lets see some pix when you are done.

The only thing I can add - is take a tripod if possible to get those group photos or those posed shots. In addition I know you can rent lenses, it may be worth the time to get one a week early to practice with as the lens you have may not get up close for those intimate shots, I believe unless you get real up close , a zoom lens may be a good idea to capture those moments. I am not a wedding photographer, this is just a couple of things I should have done when my sister got married, she fortunately had someone else do the photos for her, but I was the backup, and I noticed the differences from what the pros did to what I did . , Was a great learning process and eye opener on how well prepared photographers must be when they work in that business.

Charkra: Great addition, bring a tripod. They are especially helpful when doing available light shots from the back of the church, if the wedding is in a church. Many churches do not allow flash during the ceremony. Also the zoom lens, if available, is another good addition.

Guest wrote:
[quote]1. Make a list (in order) of the shots you need to take, and what special (if any) shots the bride would like you to take. quote]

I am not a professional photographer but have done bridal showers and other type of engagments for friends and family.

One of the first things that I learned was to ask whomever you are taking photos, what family group shots are importantant to them.

Wish you the best with this job and let us know how it turns out.