Settings for shooting nighttime Christmas lights with 5d3

Use the previous responses as a general guideline and shoot away.  The lovely thing about DSLR's is the instant feedback and shoot-again aspect.

Try some fun stuff too:  background blurred lights with a pine tree or person in the foreground.

When in Manual mode with ETTL flash, you can set for 1/4s at f4 and the flash will give you a short quick burst to properly illuminate your foreground subject, with a nice, full 1/4s on the background leaving nice blurred xmas lights.

Once your exposure is 1/4s or slower, try handholding and shake the camera or do a quick tiny circular motion to get some great light effects.  Do this on your home xmas tree as well.

Also, with a  1/2s exposure, handhold and pull your zoom from wide to tight as you release the shutter for a Star Trek Warp Drive Effect.

Go out and play!!!  You'll impress your friends with their ho-hum ordinary iPhone attempts.  

Jim