You should demonstrate excellence in all of your academic subjects. Though you can be stronger in some subjects and weaker than others, you should be an exceptional student in almost every class.
Don't be discouraged if your GPA isn't quite as high as you wanted it to be. If your grades have improved from your freshman year until the time you apply, officers will be impressed, and if there was a dip in your grades because of a personal situation, you can explain it in your essay.