First, you need to fill out official Russian Visa form that can be download from Russian Consulate site. Russian Visa download page
Second, USA citizen requires to have valid US Passport which is not going to expire before Russian Visa expiration date.
Third, you need to pictures with the following sizes: 1 3/8" X 1 3/4" with the head centered in the frame.
Finally, you need to cut a check or money order for the following amounts
Single Entry or Double Entry Visa:
$140 - 10 business days
$250 - 3 days
Multiple Entry Visa:
$150 - 10 business days
$450 - 3 business days