If you want to get a visa at the invitation, you will need to provide documents from the American side, if you chose the purpose of their trip. The list includes the invitation or specific businessinvitation (if you go to USA for work; copy of passport or card of resident of the US; be sure to share photos as proof of your direct acquaintance.
The procedure for obtaining invitations and visas it is simple and takes a maximum half an hour. But you will avoid a mere formality, but the interview at the Embassy or Consulate where you can ask questions related to the host and to elucidate the accuracy of your information. How much do you know about those who you invite. For example, questions such as:
what is your connection with the host side;
- who exactly is inviting you and on what terms;
- the place of your actual residence in the United States.
Of course, the timing of applying for a visa neither more nor less dependent on inter-state relations, from the practice that prevailed between the countries of the required passports, travel purposes, etc. And on arrival at the site, you again have a similar procedure of interview with the representative of the United States. The questions are similar, and in principle, you shouldn't be surprised that they will be set in English about the purpose of the visit, about who you will meet, how long you plan to stay, etc.
By the way, the visa invitation in USA – the most popular visa is requested at the American Embassy. And documents from the inviting party, – a required element of its design. And if you invite relatives, apply confirming the family connection document. Then the problems with the visa will not.