Employers want to know details about your past jobs and what you accomplished. Highlight the tasks you were responsible for that relate to the job you are applying for. Job titles by themselves tell the employer little about your experience. But too much detail can be worse. List tasks so they effectively tell the employer you are right for the new job.
You probably have a laundry list of tasks you performed on a daily basis, but only some of them will have real value to a new employer. Scan the job posting and use a highlighter to mark the tasks and action verbs the employer seeks. These are the tasks you want the employer to see you have experience with. List similar tasks you performed on your resume, using similar or the same action verbs the tasks you list.
White space makes a resume attractive and readable, so don't pack too much text into yours. Include up to four lines to describe your tasks and format them using bullet points. You want your tasks easy to scan through. Ask a friend to review your resume for 30 seconds and then check to see whether she picked up the important tasks. If now, simplify and revise. Be sure to list the most important tasks first.
Begin each task with an action verb such as "analyzed," "delegated" or "produced." Use a new action verb each time, and don't waste any precious resume-space saying the same thing twice. For similar tasks at different jobs, use similar action verbs but not the same ones. Keep the action verb in the same tense for the whole list -- choose past or present tense.
Turn your tasks into accomplishment statements. Princeton University's Career Center recommends writing accomplishment statements using the "APR formula" or action-problem-result formula. Following this formula, each task begins with the action you took, names the project or problems you acted upon, and specifies the result. For example, you could say that you, "Designed a more efficient database system that reduced reporting errors by 60 percent."