What precaution must be observed when working with alcohol?

There is no indication in the question as to how much alcohol is being used. Assuming a large volume, I suggest the following:

As alcohol is a flammable liquid that gives off fumes, the main precautions are: no naked flames, and work in a well ventilated area. Other precautions would be to wear surgical gloves, and goggles for eye protection from splashes. A foam fire-extinguisher nearby is a sensible precaution too.