A cover letter is apparently a great chance to demonstrate your personality. Normally, there are 6 kinds of Russian visa. Make sure the passport details match the passport used for the application for instance, if you're likely to change out your passport shortly before the trip, you will need to wait to use the particulars of your new passport, as that is the one in which any visa is going to be affixed. As other forms of visas aren't as prevalent, I won't cover them.