Ensure that your documents are correct and complete before you commence your journey. Delegates must register for the event before applying for a VISA. Once you have registered for the meeting please contact the Registrations Department in order to obtain a letter of invitation.
For more information on visa requirements, please visit the website of Ministry of Foreign Affairs of Italy. Please keep in mind that a visa application may take some time to be processed. Apply for the visa early on to ensure its approval before the congress begins.
Check with your local embassy what sort of documents are necessary in your specific case, as this may differ between delegates from a same country.