Step 1: Camera and settings
Next is the most critical part in the whole process, set the exposure to around 4-6 seconds.
Step 2: The laser for writing
The beam itself does not need to be visible for the photo, just the beam point. This means you can use low powered lasers during the day and still take effect pictures of laser writing. Dark conditions will give the best effect though.
Step 3: The writing itself
The first few attempts will be a mess so give yourself time to practice and you'll get some pretty amazing results.