Provide employer context
It is essential to describe the companies you have worked for, especially those that are lesser known. During high school and early in college, I worked for a couple small marketing companies. Both experiences deserved attention but most Human Resources people were unfamiliar with them. A bullet describing the employer and what they do will give more context for readers. Keep it short because too much can detract from your accomplishments.
Include some personality
I am not saying pull an Elle Woods (remember her? The perky protagonist of "Legally Blonde"?) and make your resume pink and perfumed but including hints about your interests outside of work shows that you are a well-rounded person. I found that there was room in my community service section and when I mentioned my study abroad experiences. These items on your resume also give your interviewer a chance to talk about experiences you have had that will set you apart from other candidates, and may make you more memorable. Talking enthusiastically about something you have done is a great way to show what sort of energy you would bring to a job.
In my opinion, this is the most valuable tip. Everything you include on your resume must prove its relevance. How do you do this? By showing measurable results for your successes. Provide numbers to represent the effectiveness of something you worked on. For example, you planned an event for a school club that had 450 people attend, make note of it. Actual figures are memorable. If numbers do not seem appropriate, mention what eventually became of the project. Maybe you earned an award or made a presentation to a large group of people. Showing results for your work will definitely make you stand out.
It is also fine to customize your resume for each position you are seeking. Highlight the aspects of your experience that you believe will be the best fit, and be clear about the assets you believe you can bring to an organization. And don't forget to proof read carefully. Misspellings and grammar mistakes really do reflect poorly on you, especially if you list as one of your assets that you are "detailed-oriented." Remember, it is never too early or too late to be revising your resume. It is a constant work in progress.