Find an accredited sound design course. Many reputable colleges and private institutions offer courses in sound design. Typically these will involve modules in recording and technology, songwriting and composition, performance and looking at how sound is affected by its environs.
Visit the college that you feel offers the best course. Ask to see the studio equipment and make sure it is state-of-the-art. Anyone looking to employ you after you graduate will want to know you are comfortable using the latest technology.
Set up your own studio. A computer (250 GB memory, 1 GB RAM), music software package (Cakewalk Sonar studio for PC, Apple Logic Pro for a Mac), MIDI interface, mixer and microphone are all you need to set up your own bedroom operation. Use your bedroom studio to experiment with soundscapes and different genres of music. Invest in a film editing program such as Final Cut and practice laying down soundtracks to films.
Read about different acoustic treatments. Find out how diffusers, which are used to break-up and disperse longer sound waves, and absorbers, which are used to cut down on echo and reverberation, help improve the acoustic quality of a room. Experiment with making your own diffusers and absorbers for your bedroom studio. Understand how different densities of material impact on the quality of sound.
Collaborate with people at your college or friends at home. If you know some people in bands, offer to record some tracks for them. If you know some aspiring filmmakers or theater directors, ask to help out with their production. Build as many credits to your name as you can before you finish college.
Apply to do some work experience at a music production studio. Offer your services for free and the likelihood is that a studio will take you on. You will get to see how a professional studio works and they might even offer you a full-time job once you graduate.