You want to start by giving yourself a super slow shutter speed. Mine was 15 seconds, so I had lots of time to write entire words. But it depends on what you want to write, so that’s for you to experiment!

Then, make your f-stop/ aperture suuuper small - mine was f22, I think. This made the images really clear, but you can open up the aperture more to get blurry effects. 

You don’t actually have to do those two in any order, but yep that is how I did this. Make sure your camera is in a secured, still area so the image doesn’t get too blurry. Also, great tools to use are flashlights (what I used) and glow sticks and any kind of flame. :)

Hope this helps! :)