The good people in the personnel or human resources department are not the buyers - the ultimate hirers. Unless you are seeking a job in the personnel department, these people are not making the hiring decision. The hirer are the managers in marketing, manufacturing, information technology, sales, and finance. The job seeker will be hired or rejected by the people for whom and with whom he or she would work. The actual hirers are your customers - the people to whom you must sell yourself.
The personnel department is a screen, a gatekeeper. Part of their job is to keep unwanted, unexpected, unrequested resumes from cluttering managers' desks. Unless the personnel people are alerted to a specific hiring need, they do not carefully review and study resumes and job applications looking for the next superstar. In fact, the personnel department views most nonspecific resumes and job applications as time wasters.
Even when the people in human resources are looking for a certain type of potential employee, their selection process starts with rejection. Particularly when a job opportunity is advertised, personnel people often face stacks of resumes to review. Their goal is to dramatically reduce the stack. They scan resumes looking for reasons to reject candidates. Resumes are tossed because of a candidate's school, affiliations, geographical location, or job history. Resumes are rejected because the reviewer is weary or thinks he has already found the perfect candidate, or because he misreads the write-up.
People in human resources, especially early in the hiring process, hire by the book. The book is the written job description. Good candidates are routinely rejected because their background doesn't seem to precisely mirror the job description. The human resources department wrote the job description, or participated in the writing, so anything in the resume that is even slightly off the job description is cause for rejection. The actual hirers are more flexible, meaning that they commonly hire "talent" and refit the job to match the talent.
Starting your selling approach at the personnel department means you don't know who your customer really is. It means you don't know wy the company should hire you. It means you don't know who in the company will benefit from hiring you. Consequently, your cover letter will be general, and your resume will be non-tailored. You are then dependent on one person in personnel to properly interpret your resume, translate your resume into relevant value to the company, and then voluntarily send your resume to the head of information systems with a note saying, "Hire this digital video expert immediately." That doesn't happen.
The human resources department is important. They are expert interviewers. They give and interpret tests. They handle all post-hire administration. Their opinions are valuable and considered. But, almost always, the hiring decision is made elsewhere.
Start selling yourself to that person who will recognize and need the value you will bring to the organization. Start with the CEO or the head of manufacturing or the vice-president of sales. If the job opportunity is advertised and the hiring company is named and the job looks right for you, use the advertisement as a lead. Study the company. Do your homework. Send the proper hiring person an impact letter, and get an interview.
The personnel department is much more helpful to you after you've been hired.