Advisory Opinion Letters aka Reccomendation Letters are usually included in an application. These are most often drafted by your lawyer or you and then sent to the person to review, print, and sign on their letterhead.

USCIS does not have a minimum or maximum number of letters they ask for so it is really up to you. Most people submit anywhere from 5 to 12, the average being somewhere on the higher side like 9-10. The letters should come from experts in your field, people who have worked with you and can vouch for you. A tip in this part of the process is to also include press about them so as to prove their credentials and avoid multiple letters from your academic instituion.

It is important to start early in this process and begin scraping the internet for your name and saving and downloading anything and everything you find about you. Lawyers will ask you to provide press about your work and accomplishments from major newspapers, journals etc. While it is valuable to have 2-5 articles that do this it is also valuable to show press that includes announcements of your exhibition, brochures of shows you have been part of or articles talking about projects that you were part of even though they do not mention your name. In these cases experts from your field could vouch for your involvement in projects or exhibitions in their letters by briefly mentioning them and your role.

The Itinerary is an important part of your application and can be completed once you have all your work engagements ready. It is helpful to create an excel document with the months and years to notice overlaps and see whether you are in fact covering the entire period allowed. These are relatively more simple for those that have galleries acting as agents. For others it can be daunting to have to collect promises of work for three years when often young creatives do not even know what will happen next month.

While it is good to have commitments from people you want to work with, it is also not required of you to fulfill all your commitments and it also allowed for you to add engagements and or alter the itinerary during the course of your O1 approval. Each engagement in the itinerary is accompanied by an oral agreement/deal memo.

Deal Memo's also known as oral agreements or contracts are between you and another person, organization or company showing that they want to employ you for your extraordinary ability. These do not legally have to be signed, however the more official you can make them the better. You should include who will be employing you, during what period and how much they will pay you. You should also include where the work will take place and the nature of the work. Providing a background of the employer/organization is also a good thing.

One of the main things to keep in mind when seeking a multiple-employer itinerary based visa is that you want the work engagements to cover a period of three years, the maximum duration you can get the O1 for at a time.