Not many people like to hear criticism, and even fewer like to hear it from the ones who they love. But this is where you will gain the most true and significant understanding of your strengths and weaknesses. Call three or four of your closest, most trusted relatives and friends into a room with you. Ask them to honestly give you feedback on you as a person. At first, they may be reluctant to comment about your undesirable traits, so make sure that they understand that this is for your personal benefit. Bluntness is best in this situation.
Write the criticisms on a pad of paper. Ask for specific examples. Do not argue about controversial points or gush about nice remarks. Just get the feedback down on paper. Thank your loved ones and conclude the meeting with a positive attitude.
Sit by yourself and look over the comments. Check off the ones that you agree with, and think about the ones you disagree with. Did they come up more than once from different people? Look at the examples. Could these be legitimate weaknesses that you need to work on? Consider the people who voiced the comments: folks picked for being the most trustworthy people you know.
You might disagree with a strength, such as "You're nice to everybody." To you, that might be a weakness and something you need to work on as well.
Many people don't have the ability to see their strengths and weaknesses. Consider video-recording yourself and your interactions with family and friends for a week. Then watch the tape. You may be able to see some of the issues that your family members and friends brought up in the focus group.
Be honest with yourself after reflecting on the feedback of your loved ones. The weaknesses that you have a hard time admitting to yourself could be the ones that will make the biggest positive impression when brought up in an interview setting, as long as you put the right spin on it. For example, if you identify one of your weaknesses as being "too controlling," your spin is that you sometimes come off as controlling because you like to monitor an idea or task closely, from beginning to end.