Following on that, you should try to demonstrate an interest in economics or business, or in how they relate to your chosen field of interest. If you are interested in Media and Entertainment, sit down and try to work out how going to business school would help you advance in that field. It's important to remember that B-Schools see themselves as a means to an end, not an end in themselves. They want students who are ambitious and plan to use business school to get them ahead in their chosen fields. They DO NOT want students who are applying to business school because they want the credential on their record, or because they don't know what they want to do and need more time to figure it out. That being said, B-School is full of those kind of people (who have no idea what they want to do yet), but all of them managed to tell a compelling story on their applications about how business school was the right place for them and how it would help them in their careers.
Try to display initiative and become a leader in an area that interests you. Try to become the head of a club, the captain of a sports team, the editor of a magazine, or the director of a movie. B-schools will look for that kind of engagement and "management" experience. They want to know that you are good at interacting with people, that you have some "leadership" skills, and that you are invested enough in what you do to want to take ownership of it.
Now, about work experience. It used to be the case that very few students came straight from undergrad programs into Business School. Although schools now seem to be admitting more and more students straight out of college, it is still rare and you may find yourself struggling with many parts of the application. Each application asks specific essay questions about "leadership" and personal experience, and the more varied and interesting your responses, the better your essays. Since most undergrad programs are similar, it will therefore be harder for you, as an undergrad, to put the same amount of color and diversity into your application as someone who has been out of school for a few years. It will also be difficult for your to argue convincingly that you understand how business school fits into your career, not having begun your career.
I would strongly advise looking for a summer internship at a company or NGO in the field that you are interested in during college. I would also strongly strongly advise trying to find a job in your field for at least 2 years after college before considering school. For many people, Business School IS NOT an intelligent choice. If you already have a great job at a company you like, with opportunity for upward mobility, why spend $200,000 for a school that at best can only send you back into the same field with a small promotion? I think business school is best for those who are interested in changing careers, or who have reached a ceiling in their upward momentum and need business school to help them take that next step. I feel the situation is slightly different in China, where graduate education is becoming more and more of a basic threshold for employment, but in the US it is certainly worth trying to succeed on your own before spending a lot of money to do so.
Those few years after college will also give you a chance to become a more well-rounded person, to travel places you've always wanted to travel, to see things you've always wanted to see, and to take some risks that might be harder later in life. Start a company, write a book, move to Peru--even if you fail, you will be demonstrating to schools that you have a passion and are independent and ambitious about pursuing it. And if you succeed or discover something new that you really love, it will either give you a great story to tell on your application or maybe even make you so successful you don't need to apply at all!
If you finish college and you have a really strong idea that B-School is the place for you, then by all means, apply. Consider looking into the growing number of special scholarship programs B-Schools offer for students coming straight from undergrad programs.
Basics about the application:
Business schools considers the following: your transcript, your GMATs or GREs, your essays and your recommendations.
Transcript: pretty simple here, get good grades! But also remember that grades aren't quite as important to B-School as other grad schools. The average GPA is usually somewhere around 3.5.
GMATs/GREs: Personally, I took the GMATs, but GREs are an option too. My understanding is that the GMATs' math section is a little harder, while the GREs' verbal section is a little harder. Take whichever you feel most comfortable with but make sure you study hard and do well, as this is by far the easiest part of the application.
Essays: And this is the hardest part of the application. I applied to five schools and had to write somewhere around 40 essays by the end of the process. These will take endless drafts and revisions. Since you are thinking so many years ahead, my advice would be to start practicing now. Not seriously, yet, but take a moment every once in a while to jot down essay ideas. Try to remember the important moments in your life, what you felt and how they changed you. What is especially meaningful to you and why? The more you practice, the better a writer you'll become. The same subjects that make good essays might make good blog postings, diary entries, or even publications in a student journal somewhere. Consider those options as a way to practice. When you start applying for real, make sure you send your essays to be read by friends who are in business school already. They will know best what makes a good application essay. The more people who read your work, the better it will be.
Recommendations: B-schools discourage applicants from using academic references, although this must not apply for undergrads. Nevertheless, consider looking for a mentor at a summer job or internship who might help advise your career and eventually write you a recommendation. The schools want to see who you are as a person, as a worker and as a colleague, not just as a student.
About applying and the process:
Start early, in January or February before the year you want to apply. Take the GMATs and get them out of the way, giving yourself time to retake them if necessary. If you are really well prepared, you could take both the GMAT and the GRE, and send only your best score, that way avoiding having to send two scores if you mess up the first time. Start researching schools and get an idea about what makes them different. Although B-schools all claim to be unique, I found them to be quite similar in terms of on campus offerings. One big difference, however, can be what sort of access they give you off campus. Make sure each school is known by recruiters in your chosen field and that they have a good track record in placing students in that area.
Start your essays early so you can get several rounds of revisions done for each. Your goal is to have everything wrapped up by the end of July so you can make the Round 1 application deadline for every top school on your list. This will give you a slightly better chance of being accepted and also give you the opportunity to apply to safety schools if the first round doesn't go well. Keep in mind that the application process is quite time intensive, and most people I know only applied to a small handful of schools, like five or six.
Try and visit as many schools as you can to see if you would enjoy life on that campus and in order to become familiar with specifics of the schools that you can use in your essays. Try to meet and talk to students, either on campus or through your school friends and alumni, as those one-on-one conversations can become useful material in your applications.
Then the waiting begins. You sit and wait for interview invitations. An invitation to interview is a very good sign, it means the school likes you, is strongly considering you, and is now ready to meet you. Most top schools require interviews in person in order to offer you a place in the class. To prepare for these, keep working on your story. Why Business School? Why Now? Why at School X? Call on your research into the subtle differences between each program, and your experiences with students from those schools and during visits. You usually have the opportunity to attend a class or two on the day of your interview, so if you schedule your interview for the late afternoon, it will give you a chance to look around campus and have a very fresh impression in your mind when you go into your meeting.
Try not to get discouraged. The waiting process can be long, and you may be rejected from schools you were confident about or accepted to schools you never dreamed would take you. Try not to think about it too much and try not to compare yourself to others. In the end, it is your unique strengths that will get you into school, not your similarities to the rest of the class. Just because someone has a low GMAT score doesn't mean they don't have a high GPA, amazing extracurriculars, or are just a fantastic and charismatic storyteller. It's impossible to know the details of everyone's application, so don't try. You will be a happier and less-stressed applicant if you try to put the waiting out of your mind and focus on the things you can control, like preparing for interviews.