To get into a bachelor's program, you will need good grades in high school and high marks on the SAT. Take as many science courses as you can, and if you learn a foreign language, try to choose German or Japanese. You'll also need to take the TOEFL if you aren't from an English-speaking country.
Some extracurricular activities that the university may look for include computer gaming and programming, astronomy and model aircraft building. Having any experience with piloting or flying also helps.
While your grades in your BS program will count, you will also need to take the GRE, provide a minimum of two letters of recommendation and write at least one essay.
Some classes you'll be expected to do well in are linear control systems, structural analysis, orbital mechanics, telecommunications, vehicle design and flight mechanics.
You will also have to take standard science courses, such as chemistry and physics, and a number of higher-level math classes. You will also be required to take several classes in the humanities (at the bachelor's level only).
Unlike some other engineers, aeronautical engineers are not required to get any governmental certifications.