You have one page to prove to a potential employer that you're worth hiring. Don't waste time transcribing every task you ever carried out. Highlight how much impact those tasks had for the company.
Photo by Flazingo.
As advice site Muse points out, there's a big difference between the work you did and the effect it had. Sure, you can say that at your old job you made phone calls and acquired new clients, but it's a lot more impressive to say that you pulled in three of the top five clients at your company. The tasks are menial, but the impact is what catches the eye:
For example, say that as part of your current marketing role, you helped redesign your company's Facebook page. You could describe the activity on your resume simply as: Designed cover photo for company's main Facebook page. Yawn. If you dreamed up, pitched, and fought for the look of the page to go in a specific direction, such a statement would fail to capture your role in the larger branding strategy. Underselling your achievements is as bad as overselling, and it's a resume, so don't. To fix it, don't just list the tasks you completed, but also be sure to provide insights into the impact you had.
Keep in mind that your potential employer probably knows the specific tasks associated with your job already. That's why saying you can use Microsoft Office isn't all that impressive. It's ok to mention the skills you have if they're relevant to the position, but if you really want to stand out, highlight how you used those skills instead.