The frequency of cleaning depends upon the material being processed. For wood or anything that gives off a lot of smoke, you might be cleaning it daily. After one to two days of typical operation, you should clean your system.
For cleaning the lenses, there is special lens cleaning tissue and lens cleaning solution that is friendly to the coatings on the laser optics. What you don’t want to do is to scratch or any way degrade the laser optics (mirrors or lenses).
For general cleaning on the outside of the machine, you can use a natural cleaner.
-Mike Fruciano, Coherent