This is most always the first question and quite possibly the most important question in an interview. How you answer this question sets the tone to how the interview will go. Make a misstep with this first question and you may lose the interviewer's attention for the rest of the meeting. In order to set you up for success when answering this vital question, I want to address what you want to avoid.
DO NOT offer any personal information.
The question itself is misleading, the interviewer specifically asks you to tell them about yourself. However, they really don't want to know where you grew up, if you are married, how many kids, dogs, and cats you have, or what you like to do in your spare time. What they want to know (and how you should answer) is what skills, experience, and knowledge do you have for this job?
DO NOT ask them what they want to know.
You may think that by asking the interviewer what they want to know about you, you are simply trying to focus your answer. However, what the interviewer sees is someone who did not prepare. This is one of those questions that you should write down and practice until you can deliver it naturally with poise and confidence.
DO NOT "wing it."
Although most hiring managers use this question as an ice breaker to make you feel comfortable and ease into the interview, they are also making judgments based on your answer. They want to assess your communication skills, they type of impression you will make, and how you can handle an "unstructured" communication environment. Going in unprepared is simply not an option if you want to make the best first impression.
DO NOT talk to long.
Be brief, concise and succinct. Highlight a few of your strengths, but don't tell your life story. I once asked this question in an interview and the candidate talked for 15 minutes! Hard as I tried, I have to say my attention waned around the 5-minute mark. As a general rule of thumb, try not to talk for more than 2 minutes at a time in an interview.