Under U.S. law, all applicants for nonimmigrant visas, such as student visas, are viewed as intending immigrants until they can convince the consular officer that they are not. You must therefore be able to show that you have reasons for returning to your home country that are stronger than those for remaining in the United States. “Ties” to your home country are the things that bind you to your home town, homeland, or current place of residence: job, family, financial prospects that you own or will inherit, investments, etc. If you are a prospective undergraduate, the interviewing officer may ask about your specific intentions or promise of future employment, family or other relationships, educational objectives, grades, long-range plans and career prospects in your home country.
Each person’s situation is different, of course, and there is no magic explanation or single document, certificate, or letter which can guarantee visa issuance. If you have applied for the U.S. Green Card Lottery, you may be asked if you are intending to immigrate. A simple answer would be that you applied for the lottery since it was available but not with a specific intent to immigrate. If you overstayed your authorized stay in the United States previously, be prepared to explain what happened clearly and concisely, with documentation, if available.