This is a common question. As a long time interviewer, I look for candidates who are realistic about their strengths and their weaknesses. Because our greatest strengths can also be our weaknesses, it is always good to answer this by taking something what you can do well and see how it could become your greatest weakness. That way, it puts a positive light even on your weakness. For example, if you are passionate about the work you are doing and always want to the best job possible, you might say that even though this is a strength, that sometimes you might be too hard on yourself when you don't meet your own expectations. No matter what you say, it's also always good to follow up with a comment to your interviewer like "but this is something I have become aware of, and so I'm working on that and really paying attention to it".
Read about this kind of question and the best answers to use at monster.com or careerbuilder.com. I would suggest something along the lines of "I am impatient with others who don't respect the urgency of this kind of job etc etc" or "I tend to not delegate as well as I should. I want to make sure things are done right". Do not tell them you are lazy or easily confused if you want the job.