Decide on a company name. As a music publisher you will need to have a name to receive payments. You do not need to have a limited liability company. You can simply go to your local government business authority and get a DBA license, or "doing business as." This will enable you to take payments in the name of your company. Just give the information to your bank and you will be able to cash checks in your company's name.
Prepare your music in digital audio format and sheet music format. This can be done with tools that most people already have on their computer. Take the physical recording of your music and extract the files using a program like iTunes. Save the file in an MP3 format to create a downloadable version for your website. For your sheet music, you can either copy the music by hand or use a notation program to create your scores.
Copyright your music. This can be done for a fee by sending your music to the Library of Congress. Copyrighting your music protects you in the case of someone stealing your music. If you have an album, you can copyright the entire album for the fee of a single work. As of August 1, 2009, the fee for registering a work online is $35.00 and for mailing in a physical copy is $65.00. Mail or upload all of the requested documents to the address located in the copyright form. There is a different address for each type of media. Audio CDs are okay, but do not send CDs with PDF files. The copyright office requires a hard-copy format of all sheet music.
Determine whether you want to join ASCAP or BMI. Both performing rights organizations operate by collecting royalties for your music that is performed on radio, television, the internet and in live performances. They will represent you in case of copyright infringement and work to collect money that is owed you.
Create a website to distribute your music. There are places that will prepare a website for you such as CDBaby, or if you have experience creating websites you can create your own. If you create your own, you will need to have a webhosting service. Many independent publishers will list their works online along with sample recordings and provide a contact form for clients to contact them about purchasing music. Payments can then be taken online through Paypal or Google Checkout after which you must then manually deliver the score to customers through email or postal mail.
Find a music distributor for your recorded albums. This will enable you to get your music listed in iTunes, Amazon and several other online music distributors. CDBaby and Tunecore both have options for submitting your music to digital distributors.