How to answer this common interview question without sounding doubtful or conceited.

Interviewers have been asking this common question for decades and many potential employees still get hung up answering, even though they may know it is coming. When employers ask this question to potential employees, they are looking for a few things, and the answer to this question has more to do with the thought process behind it, than the answer itself.
Here are a few tips when being put on the spot to answer this question.
Choose a strength that coincides with the role you are interviewing for
If you are applying for a role as an accountant, the employer will not want to hear about how you are an amazing swimmer and that being an athlete is a strength. Although that may be a strength you are proud of, it doesn’t really help you be a better accountant.
Look at the job description and pick something that will help you succeed in the job
Matching your strengths to a part of the job is how you can set yourself apart from other candidates, and it may help you if you are not as confident in a certain part of the job you are applying to. If you are applying for a technical job where you may not have all skills required for the role – picking a strength that highlights your soft skills can help supplement your overall candidacy.
Clearly explain how your strength relates to the job
Does the role require interaction with customers? Is it technical? Does it require creativity? Start by answering the question with a part of the job you feel your strength will benefit.
“I see that this role requires record keeping, and I know one of my greatest strengths is attention to detail. In my past professional roles, my detail-oriented focus helped everyone on the team stay organized and contributed to our overall success.”
The same rules apply when picking a weakness, as a strength
Employers are looking to see if you are qualified for the job. They are also looking for indicators that you can be trusted to handle all new tasks and challenges. Your honest self-assessment could go a long way. Some feel that you should pick a non-essential skill and match that with something that may not apply to the job itself, but honesty is the best policy to sound sincere.
Take a look at the job description again and pick a weakness that you may have, against a skill set that may be required
How does that weakness effect this role, and most important – what you have done in the past, or plan to do to overcome that weakness. Using the organization example from above.
“Organization is something that I have struggled with in the past, and I know it is a key part of this role. Knowing that this is something I need to work on, I have taken steps to improve; including time blocking my calendar and using 20 minutes each day as office time to clean my workspace and make To-Do lists which have increased my attention to detail and productivity.”
Instead of a generic or non-essential skill as a strength or weakness, using an example that will help supplement the role, or be honest about your flaws will not only show your personality and thought process, but will make you more approachable and show you are prepared for anything!
That is the thought process behind the question that most employers are looking for. Being asked to brag, or be humble about yourself can be weird, but it is no different than being confident about your other professional skills, and honest about what you want to work on in your next role.
Combining all the tips above in a seamless, prepared answer, will give you an advantage over other candidates and impress your future employer!