1. Don't rush your application. Unless you're in a particular hurry to get your MBA, be sure to improve any "weaknesses" you feel you may have before applying. For example, if you're not comfortable with your English language skills, don't invest your money in the GMAT and the school application fees, yet. Business school applications are soaring in America, and you will be competing against native English speakers who grew up in this economy and culture. Aim for complete fluency.
2. To improve your written English, I heartily recommend reading The Economist magazine every week. I don't necessarily agree with all their viewpoints, but it is the most eloquent business magazine around, and its international coverage is vastly superior to that of American business magazines (which like to focus on personalities and big names). Reading The Economist every week will expand your vocabulary, and make the reading comprehension portion of the GMAT easier.
3. Take an accent reduction course, especially if your accent is non-European. I'm not saying this to be insulting. I am half-Asian, and have lived in Japan and Taiwan, and I heartily embrace foreign cultures. I am simply being honest: American schools may be liberal in admitting foreign students, but American companies will discriminate against a foreigner with a strong non-European accent. I'm sorry this is the case. They will hire you based on your credentials, but when it comes time for promotions, your accent will be seen as a "liability" if your job entails making presentations. I recently sat in on a biz school class, and a foreign student made a comment in class. His accent was so heavy, that other students asked him to repeat himself. When he did, they pretended to understand, and quickly moved on to the next student. Another friend of mine, a very intelligent and capable Malaysian MBA holder, was rejected from a job after her oral interview -- even though she had made it several rounds into the recruiting process. In respect for your feelings, no one will tell you your accent is too heavy; it's your responsibility to make sure you come across nearly accent-free. (A friend of mine suggests that foreign students acquire an educated British accent, since most Americans associate a British accent with sophistication and intelligence.)
4. Take a speed reading course. If you think reading English now is a drag, imagine the reading loads you'll get in an American graduate school.
5. Develop outside interests beyond work. International students have the reputation of being very book smart (having high GMAT scores and grades) and hard working. However, they are not known for having strong outside interests beyond golf, travel, religion and families. In particular, American business schools smile fondly upon any charity work or community service. If you don't have any active charity work or community service on your resume, you might consider postponing your application and spending a year or two getting involved at least part time in a benevolent organization.
6. Consider applying to lower-ranked private schools. Everyone loves the top 10 schools -- and I congratulate you if you succeed in getting in! But you can also get an excellent education at a lesser-known private school, and if you scored well on the GMAT, that private school might award you with a full scholarship. Due to our nation's tax crunch, public universities are unlikely to award scholarships to international students, and the top universities often award aid on a need basis only. Schools such as Notre Dame and Tulane, on the other hand, are more liberal with their scholarship assistance, especially if you have a top GMAT score.
7. Pick your city well, and not just the school. I think Los Angeles is a great place to go to business school: the weather is always moderate, both winter and summer, and international students can find all their favorite foods and media from home within a 30-mile radius. The only problem with Los Angeles is that you really need a car to get the most out of it. My suggestion: if you visit a campus, be sure to take your time to explore the city around it, and imagine what it's like in the winter. Northwestern has one of the best business schools in the world, but if you've never experienced a Midwestern winter, you could be in for a very cold surprise.
8. Finally, when you get to your business school, remember to network as much as possible. I notice many international students only hang around with people from their country or region. They are missing the opportunity to meet some of the brightest people from around the world. The best way to meet people and establish relationships with them is to get involved in extracurricular activities. Don't just join the ethnic or international clubs -- join clubs that focus on a professional or charitable interest, or even clubs organized just to have fun.