You must obtain a Letter of Invitation from a sponsoring company. This can be the hotel you're staying at, from friends or family in Russia, or a travel agency. Fill out the Letter of Invitation and wait approximately 4-6 weeks.
When you receive your Letter of Invitation, download a Russian visa application from RussianEmbassy.org.
Fill out the application and mail it, along with the current fee, a passport-sized photo, your Letter of Invitation, your passport with at least one blank page, and confirmation of your hotel stay or travel agency plans to your nearest Russian consulate.