Show, don't tell. That's it, that's all. Same advice for every genre of writing, folks. When you show readers what you want them to perceive, and allow them to make their own conclusions or labels, based on the evidence you provide, then you give credence to your readers' intelligence and challenge them to think as they read your words. If you spoon-feed readers with "telling" sentences like "I learned to take initiative during my first job, and I earned the respect of my fellow employees," you dictate what they should believe about you, but never truly make them believe it. "Telling" words not only leave no memorable images in their minds, but also leave readers wondering whether you can even prove your assertions with vivid examples.
When you write an essay for school, you must back up assertions (topic sentences, theses) with details or evidence before adding your commentary. Without those details, you cannot prove your points. Likewise, if you write about your character traits in your college essay, but don't back up your claims, you won't leave any impression except a dubious one. And you won't get yourself admitted to college.
Memorable details are the key to college admission and to writing words that people want to read. Show, don't tell. That's it. That's all.