When asked, “Why should we hire you?” It is a mistake to answer, “Because I am the best candidate!” At this point, you are not in a position to say whether you are the best candidate or not. You have not even met the other candidates.
You need to say something more substantial. You need to cover your accomplishments and you need to state your accomplishments in a “prove it” statement kind of way. By that I mean, state your accomplishments with statements that prove that you have the skill and ability it takes to get the job done.
In order to do that, you need to have done your research ahead of time. If the job posting is not very descriptive, ask for a job description. Research the company by taking a look at the company website. Do some deep thinking about how you can state your skills and abilities with examples and use the words of a third party. For example: “My current supervisor, Mark Browne, has stated that I am the best employer he has ever had in the position that I currently hold.” Or, “A co-worker of mine tells me that its been a long time since she has seen anyone relate to the customers as positively has I have.” Or, “My supervisor complimented me just the other day for my problem solving abilities.”
On top of that suggestion, have stories ready to tell that prove your capabilities in three key areas: 1) Your ambition on the job, 2) Your ability to get along with others on the job, and 3) Your ability to problem solve on the job.
If you have stories ready that prove you have those capabilities, you’ve come a long way towards preparing for the job interview.