Identifying your strengths and weaknesses will help you apply your strengths where they are most useful and limit time spent doing tasks in your weaker areas. The red card/green card exercise is a great way to discover what your strengths and weaknesses are.
For 30 days, carry a stack of green cards and red cards in your pocket or purse. Whenever you find yourself fully engaged and loving a task, write down on a green card what you are doing and who you are working with. In addition, record every boring, uninspired moment on a red card, and make a note of who you are working with in those moments. When the month is over, lay all your green cards on a table, and take note: Here are your strengths, your passions, the things that make you come alive! Then lay out your red cards. These will reveal areas where you are weaker.
Exercise taken from Go Put Your Strengths to Work by Marcus Buckingham.