This is especially critical when making observations about work performance. Keep copies of examples of poor performance. Take notes or keep logs of work assigned and completed. Maintain a record from which specific incidents can be cited. Get the best evidence possible.
Hard evidence is always better than a description of it.
While a picture speaks a thousand words, the samples of errors are more eloquent. In an instance of employee violence where a weapon was used, the actual weapon is better than a description of it or even a photograph. Date all information. Be sure to keep all documentation used to support disciplinary action in a file that is readily accessible to be used in support of a grievance or other action that the employee may file as a result of the discipline issued. This file should be preserved for approximately three years from the date of the incident.