Most people try to get this job because it is a convenient one, it offers clean working environment in an office, and relatively easy list of working duties (when compared to other jobs).
But you should not point to any of that while explaining your job choice in an interview. Nor should you said you apply becasue you need a job (or money), though it is often the reason (nobody would go to work if they did not get paid).
The key is to convince the hiring managers that you really want the job.
Talk about benefits, and good things
Say that you believe to have good predispositions for the job, and believe to bring actual value to the office of your employer as an administrative assistant. Say that you prefer routine jobs, that you enjoy doing the same tasks day after day. Some of us prefer routine jobs with steady working hours, so we can leave the office at three each afternoon, and spend quality time with our families, or hobbies.
I enjoy working with the computer, I typewrite quickly, and I simply prefer routine administrative tasks in the job. I believe that I can bring value to the team in the office, and considering everything, position of an administrative assistant in a perfect choice for me.
I have just graduated, and am looking for my first job. I believe this is a good start for my career, a position where I can learn a lot, and perhaps understand more about the functioning of the business. On the top of that, I enjoy doing the tasks administrative assistants typically do, so I have no reason to go for something else.