What should I pay attention to in Canon 600D( 18-55) wedding photos?

It's best not to backlight for group photos. If it is necessary to backlight, you need to turn on the forced flash to fill the light.

The lens 1855 takes a group photo. The best setting is that the iso sensitivity is set to 100, the av file is used, the aperture is 5.6, the raw mode is used, the tripod and the cable are used for shooting, and there is no cable release. It is ok to drive shooting with a 2-second delay. If you want to shoot yourself, use 10 seconds.

If there is a lot of stray light, be sure to wear a hood, and it is recommended to add a polarizer.