How do you answer 'Describe your personal qualities that suit the requirements of this position'?

Look at the job description. Pick out key words that describe you. If you have time beforehand, make a list of the qualities they are looking for that also describe you.

They just want to know if you are a good match for the job. If you truly can't come up with any qualities that suit what they are looking for, you're probably applying for the wrong job.

Highlight any parts of the job or job description that sound like you but add positive comments to each description.

TELL the intervewer how closely you match the job description ("I'm an excellent writer." or "My great personality and helpfulness are perfect for customer service." or "I know many of the required software programs and I'm also a quick learner!" )

Are they looking for someone who has a lot of computer skills? Do you have these skills? Then go on and on about them!

They are asking what qualities you have that will make you a good choice for the job. For example, if you are applying for a secretarial job they don't care if you have carpentry skills. They'll want to know how fast you can type and how organized you are.

They want to know if you are a good match for the job. If you truly can't come up with any qualities that suit what they are looking for, you're probably applying for the wrong job.

Are you applying for a job in a law firm? If you feel that you are good with handling confidential material, SAY SO. Are you applying for a high stress job but you're good under pressure? SAY SO.
The knowledge, set of skills & related experience makes me suitable for this position.