IS 3.3 a good GPA?

I am a high school junior and my current GPA is 3.3. Is this a good GPA to get into one of the top 50 universities? How can I improve it?

A student aiming for top 50, like all students, should aim for the highest GPA possible. 3.3 would be very uncompetitive for top 20 schools, for example. I would recommend aiming for at least a 3.5. The only way to improve your GPA is by improving your performance in your classes.