Dear Sunil
I am a person who go and conduct interviews for many a firms
Infact, we ask this question that is tell me about yourself is just to reduce the tension of the candidate.
And then, when you are going to tell about yourself, just give a rough description of your family and your native place, just say I am sunil, staying with my parents/.... and coming from so and so.
Then say, about your educational qualification, that is, i am a graduate in commerce studied in so and so college
Ok then, don't go ellaborate on the above points, but then, see that what you have to tell is what is the need for the company to select you, how they will be benefitted like that. That is you can say, you are a team player, hardworker, a person with a positive attitude . Just make them understand about your positive qualites . Now, if you are working somewhere, just say, the quality for which you are recognised.
Now, secondly this question is asked as a tool of testing your english language skill also. Thirdly, their are other points, which the interviewer keeps in mind, so, they give you marks based on your answers.
Now, if you want in detail, contact me and ask me . i will give you the details.