It depends on the author, subject, and the contract being considered.
Many self-published authors are now calling themselves Authorpreneurs. Essentially they operate like a business.
Marketing for a (new author) is going to be a challenge whether one self-publishes or has a traditional publisher. Unless you have a super literary agent who can sell your book to one of the powerhouse publishers odds are you are going to have to pitch in when it comes to marketing your book.
A good place to start is getting some positive (editorial reviews) from well respected sources, offer to speak at book clubs/events, sign up for email alerts on radiogueslist.com, write blogs/articles which feature your bio and the name of your book, join various LinkedIn writer's groups, Meetup.com.
If your subject is within the self-help genre you could write a proposal and present it to the Continuing Education department for your school district. You would teach a 2 hour class around your book's topic and charge each student a "material fee" which is actually the purchase of your book.
If you're not so much as the "go getter" type then you might consider hiring a BOOK publicist for a couple of months who specializes in books in your genre. This however can cost you anywhere from $500 - $8000 per month depending on the services you desire. Some will submit multiple press releases and provide you with a list of inquiries they receive from newspapers, magazines, radio stations, and any TV shows who are interested in getting a copy of your book for review or to possibly interview. You would then contact them and send out your book as well as follow up. Other services offered would involve the publicist scheduling interviews (for you) and mailing books on your behalf.
However you probably should not invest in a publicist unless you have some noteworthy reviews. I wrote an article awhile back for self-help/how to genre authors looking for ways to earn additional money while promoting their book. Best wishes! https://hubpages.com/literature/Authorpreneurs-Is-...