Preparation - Many job seekers make the mistake of showing up to an interview unprepared. It is very important to do research on the job for which you are applying, even if you have never done the job before be able to speak intelligently about the job position.
Body Language - When going on a job interview, you can make the mistake of sending bad signals to your job interviewer by yawning, checking your watch, sighing, or shaking your leg. You do not want to send a signal to the interviewer that your are tired, bored, or in a rush.
Bad Communication - Often during an job interview people tend to interrupt the interviewer. This is not always intentional but it can hurt your chances of getting the job.
Being Dishonest - Another common mistake made by job seekers is being dishonest with a potential Employer. It can be something as simple as saying "I've been working in customer service for many years." After which you are unable to give specific information after you are asked a series of question and it is easily detected by your interviewer.
Inappropiate Clothing - This is one of the most serious mistakes made by job seekers. When going to apply for a job, or on a job interview be sure to dress professional. No jeans whatsoever or sunglasses. It does not matter if you are applying for a executive assistant job or a job handing out flyers. You should wear dress pants and a dress shirt for the job interview.
Bad Resume - Your resume should be as detailed as possible and include relevant dates and phone numbers. The Resume should not only list your job responsiblities but also should show your accomplishments and what you did for the previous companies. Also be sure to tweak your resume for each position that your are applying for and use skills that are relevant to that position.
Lack of Resources - Some job seekers also make the mistake of only using one source to look for a job. This can be a local Employment agency, newspaper, or a website. It is very important to use as many job resources that you can find when looking for a job.