Those working for human resource departments for companies as diverse as accounting offices to those that are making custom furniture will tell you that one of the most important steps to securing a job is the completion of a successful interview. Not only is this a chance for the employer to get to know you beyond the writing in your resume and cover letter, but it is also a chance for you to sell yourself to them with each question that's asked. This is why it's a good idea to prepare by doing a mock interview beforehand.
When preparing for an interview the thing that will usually pay off the most is doing some research about the company that you're looking to work for and the specific job that you would be doing. If you're applying to work with a construction firm than it might be good to know that they only work with environmentally sustainable materials or the area where they usually work. Knowing these smaller details and catering your answers to the information that you find out can really make all of the difference in the world.
Make a list of the qualities and qualifications that you think the job requires. If you're applying to be a salesperson for a new concrete form business, than they will be looking for different strengths than if you're interested in working as a childcare worker or as a driver for a taxi service for example. When you're formulating your answers during the mock interview try to include as many of the points from your list as possible in a natural way. Try to include them in the experiences and anecdotes that you will inevitably tell during your interview. You might not be able to include all of the points from your list but this will definitely help you focus your answers to the most important information you want to get across.
If you really want to learn as much as possible during your mock interview than you should videotape yourself to watch later. This will show you exactly what the interviewer is seeing and will usually bring up some elements of your appearance that you might not have even been aware of. While you might not need the best posture and presence to get hired, concentrating on these things will help you present a confident and poised version of yourself.
Remember not to lose your personality when in an interview. When you've done your best to prepare and have even chosen some of your answers to popular questions in advance you can start to sound formulaic. When people are looking for a new employee for their printing company or their specialty food shop they want someone who seems easy to work with. That is usually someone friendly, interesting, and generally happy to be there.