Self-assessments are usually an important part of a performance review and employees should be as honest, concise and proud of their achievements as possible. The point of a self-assessment is to assess one's own output and accomplishments, so the key is to be factual and write in a clear voice that communicates these things proudly.
It is very important to be concise when writing a self-assessment for a performance review; this is because employees want to list all of their accomplishments in detail. Make sure the accomplishments can be easily understood.
Employees should never lie on their self-assessments or over-embellish their contributions, because this only reduces their credibility and defeats their chances of having a good overall performance review.
Employees should convey that they are proud of the work that they have done. This is because while humility is a good quality to have, employees should communicate ownership of their accomplishments. This lets employers know that the employee is passionate about their work and how they contributed to their responsibilities. Showing pride will give a good impression to employers and bid well for the employee's performance review.