What do admissions officers look for in an applicant?
That depends on the college to which the applicant is applying. Some of the larger schools, such as Penn State and Rutgers are concerned primarily with the numbers--your GPA and your standardized test scores. Regardless of your leadership position in clubs, volunteer activities, or sports under your belt, if you don't have the right numbers, you will not make the cut for such colleges (unless you are a superstar athlete).
Other schools take a more holistic approach to the admissions process. True, GPA and standardized test scores may be important, but so are the rigor of your classes (i.e., whether you are challenging yourself or taking an easier road), you clubs and sport activity, volunteer work, student government, letters of recommendation, your essay, and possible work history.
The most important thing you can do if you are wondering about what admissions officers at a certain college are looking for in an applicant is to contact the admissions department itself. The question, "What are you looking for in a successful applicant" is a fair one, and one that most admissions officers would be more than happy to answer for you. Granted, you may not know exactly what happens during the closed-door application review process, but you will be more informed than applying without that knowledge. Remember, you should look for a college that is a good "fit" for you. Part of that fit deals with whether the admissions department will look at those portions of your application that truly shine.