Taking pictures in a sacred setting can be relatively mindless, or an invitation to deeper reflection. Here are some questions you might want to consider:

Why do I want to take this picture? What am I trying to see and/or remember?

What is important about the combination of this setting and moment?

What will having this image mean to me? To others with whom I will share it?

Can framing this photo help me to see and experience this place that is drawing me in a way that would not be possible otherwise?

Flash
Save yourself some bad photos; turn off your flash! Chartres is a large, dark place. Most times the flash will make things look overly contrasty. It will not help illuminate things that are far away. You can always try taking a picture with your flash, but unless you are photographing something that is relatively close, you will disappointed. If you want a good shot of something far away, look for a postcard image in the gift shop by the west entrance.

Labyrinth
The light gets much stronger in the labyrinth area after 11:00 in the morning. Taking your pictures after that time will probably help them to be more visible!

Prayer
I find that many of my best photographs are composed after sitting in quiet prayer. The time you can spend preparing yourself beforehand is likely to show itself in the image you create.

Retakes
If possible, review your pictures before you leave Chartres. The process can be very instructive; it can also help you identify shots that you would like to take again. Think about why a picture didn't work. Consider what you might do differently to get the result you were hoping for. Go back and try once more. Then review your images. Repeat this cycle as many times as needed!

Tripod or Monopod
Once you are on site, you will be happy to have a tripod or monopod. The cathedral is dark and it is often hard to work with the available light if you are holding your camera. Having a tripod or monopod will allow you to take pictures with lower ISO settings.