A foreign citizen should have a visa to enter Russia (if there is no visa-free entry between countries). Therefore, you’ll need the invitation (tourist invitation or business invitation) to get the Russian visa.
Your passport should be valid for at least 6 months after the end of the visa.
You should decide what purpose of entry is suitable for your visit. Purpose of entry “tourism” permits to stay up to 30 days; purpose of entry “business” permits to stay longer — from 1 month until 36 months.
Please clarify in the Consulate or Visa Application Center what documents will be required for application, whether you need to bring the original document or the copy will be enough.
You need to apply for a business invitation to Russia not earlier than 45 days before the date of entry in case of Telex invitation; in case of original invitation from Federal Migration Department — no earlier than in 90 days before the date of entry.
While crossing the border keep the copies of your documents such as hotel booking, tickets, copy of the invitation; you may be asked to show them to the border officer.
You have 7 working days to register your visa through the travel company or through the hotel upon arrival (holidays and weekends are not counted).