What makes writing a resume difficult is that there are two audiences. First is the low-paid, non-technical HR clerk that receives the resume. If it gets past the clerk, it will arrive at the desk of the person that will be your future boss. Your resume has to have the elements that will please both of these people.
The most common mistake that I see is that people don't write anything for the clerk. Therefore, their resume never gets to the hiring manager. The "Objective Statement" at the top of your resume is what the clerk reads. Make sure you resume has one, and make it a good one.