Good manners are very important and can often determine whether or not you get the job. The atmosphere in the corporate job world is so much different from that in typical college jobs; once you're hired after college, you're expected to know how to dress and act. According to company recruiters and hiring managers nationwide, proper etiquette among students they've interviewed is sorely lacking. Companies not only want strong academic credentials and solid leadership skills, they're also insisting on excellent interpersonal skills and etiquette is considered a component of those skills. Employers can afford to be very choosy in who they hire due to the challenging job market, so get a head start on the competition...
Research the company - Look up the company online and know about it so the employer will know that you took interest.
Scrutinize your writing - Proofread and edit your resume/cover letters; have someone review them.
Dress appropriately for each company and industry - Be aware of dress requirements for each company; dressing professionally will help you develop self-confidence as well as gain the confidence of others. The NGU Career Center has an excellent handout on dressing for an interview and also a variety of books and a video regarding dress and etiquette.
Show genuine enthusiasm - Be natural; people respond well to this. Get excited about the job you're interviewing for - express interest