Think about what others have said about you when you're trying to come up with a list of your strengths. Remember, always back up your points with an example.
Pick strengths that align with the company's culture and goals. If you're applying to a scrappy start-up, highlight your ability to multitask and to take initiative.
The most important factor when choosing which strengths to highlight is to make sure they relate to the position your applying to. For example, if you're applying for a human resources position, talk about your interpersonal skills.
The weakness question is always the hardest to answer. Don't give a clichéd answer such as you work too hard or you're too much of a perfectionist. Try your best to stick to the truth and make sure you mention the steps you take to counter the weakness. Don't disclose anything that will make you look like an incompetent employee, such as not meeting deadlines and getting into conflicts with coworkers. Put a positive spin on the weakness but make sure it doesn't sound too practiced. An example of a weakness can be impatience, which can mean that you want to get the job done. Another weakness can be time management, but make sure you name the steps you take to beat that problem. You will look like a problem solver when you show them what you did to fix a flaw.