In today's world as in times past, those who are most successful have the ability to evaluate their own work. Being able to honestly and fairly evaluate what you have done or are in the process of doing will help you to become more proficient at your tasks, as well as help you to avoid the problems associated from having someone else point out flaws with your work. Employees who can see problems and correct them before submitting work as completed are valued no matter what the job, profession, or position they hold.
    A key element of self evaluation is knowing the criteria or standards by which your work will be judged. Sometimes this is as simple as looking up the criteria in a manual or web site. Other times this may entail asking specific questions of your teacher or employer. In any case once you know the standards you can begin the self evaluation process, allowing you to make necessary corrections to your work.
    Finally, you must understand that you will always have to perform a balancing act between actually getting your work done on time and submitting the best possible product. It will not be possible to achieve perfection, but you can always strive for excellence in the time allotted.