"Tell Me About Yourself" is the most popular way for hiring managers to start most one-on-one job interviews; get this part right and the rest of the interview will just naturally fall into place.
This is a job interview! They do NOT want to hear irrelevant stuff about where you go to watch football or your pets' names or how your child just lost her first tooth. You must get this job interview answer right!
What they do want to hear is a brief introduction to show how your career brought you to THIS point of being here in THIS room with them. This means you need to show where and how you got started, the decisions and changes you made along the way and that the role you are about to be interviewed for is the right progression for your career. And do all this in about 3 minutes!
Keep in mind: One trick to a successful pitch is to eliminate jargon or other language your target audience won't understand. This is especially important for career changers: don't rely on lingo from your previous career to appeal to new networking contacts. Focus your comments to appeal to your new audience and you'll be much more successful impressing them with your knowledge, skills, and abilities.
And that is how you construct your answer to the "tell me about yourself" command at job interviews.