Overstuffed Life says:
"Get your your tripod--you're going to need it! If you don't have one, you can set your camera on a stable surface, too. Keep the camera in manual mode and set it to a lower ISO. I used 400 for this picture. In order to get the twinkle effect, you're going to want to choose a very small aperture (high f-stop number). I went with the highest f-stop this particular lens can go to, which is f/22.
Because you are using such a small aperture, you're going to have to use a very slow shutter speed. This is why you need to use a tripod. If you don't, you're going to end up with a big blurry photo with no twinkly lights in sight! The other tip to making sure this photo doesn't turn out blurry due to the slow shutter speed is to either use the timer on the camera or a remote. I usually use a remote, but the button on mine is having issues, so I used the timer to get this photo.