When a company hires a new employee, they are looking for someone who A) wants to do the job, and B) can do the job.
Wants to do the job: Show that you want the job in two ways. First, explain how you were a good employee in past positions, through excellent attendance, longevity with the company, and a great attitude. Second, demonstrate it in the interview process by showing up on time and knowing something about the company itself.
Can do the job: Your work history is the first indicator of whether you can do a particular job. A good staffing agency will work to uncover your strengths and help present you to an employer in a way that highlights your most relevant skills and experience.