If you were the youngest person ever in the job, say so. If a client or boss or editor said you were terrific, that's fair game to include. If what you did was a first, include that. If you laid out objectives for a project and met them, explain how. Another way to indicate you are succeeding is by describing the companies you represent, their business, size and complexity.
Case studies are great.
Tell stories about how you went about doing an event or, for example, developing the first Investor Relations campaign. Or, conversely if you are overqualified. If you prefer one direction to another, emphasize that aspect of your work. Positioning is legitimate and the resume can lead a potential employer down the path you want to go. Save that for the next round.