1. Two pairs of safety glasses for the range of possible output colors/spectra your laser emits (you get 1 chance to lose your eyesight from a reflective surface)
  2. Don't trust the glasses anyway, as some long-wave IR can penetrate a few cm into your flesh to cause internal burns (imagine a sunburn in 3D).
  3. Use a metal enclosure with a web camera+filter to monitor for work-piece fires.
  4. Make sure to have a dry-chemical fire extinguisher next to the machine
  5. Diode lasers are expensive, but few know how to handle them without damage. Use a physical lock-switch to disable the laser with a key, and ensure the machine has a mushroom safety switch on the main power box.