1. Provide sufficient proof of funds: Freelancers need to provide sufficient proof of funds to prove their ability to pay living expenses and travel expenses in the United States. This includes bank deposit certificate, payroll, investment certificate, etc.

2. Provide detailed travel plans: freelancers need to provide detailed travel plans, including stay time in the United States, places to visit, accommodation arrangements, etc. This helps the visa officer to understand the applicant's travel purpose and plan.

3. Provide work contracts or invitations: Freelancers need to provide work contracts or invitations with their employers to prove that they have legal job opportunities in the United States. This helps visa officers to understand the applicant's professional background and work arrangements in the United States.

4. Provide resumes and professional qualifications: Freelancers need to provide resumes and relevant professional qualifications to prove that they have the ability and experience to engage in relevant work in the United States.

5. Prepare for an interview: freelancers may need to attend an interview when applying for an American visa. In the interview, the applicant needs to clearly express his travel purpose, work plan and personal situation, and answer the questions of the visa officer.

In short, when applying for an American visa, freelancers need to provide sufficient proof of funds, detailed itinerary, work contract or invitation letter, resume and professional qualification certificate to prepare for the interview. These measures help to improve the success rate of visa application.