Press releases are not the easiest to write but practice makes perfect and once you hit publish you should get a lot of practice. Contact the media as often as possible without harassing them. Comment on stories. Become a part of the local literary scene. Attend events that the media are going to be at as well. Make sure you are visible and if possible study up an subjects surrounding your book so that you can discuss them at these events.
Start with the press releases. Your first one should be the announcement of your book however it shouldn't stop there. Any time you hold a signing or will be at a fair or festival make sure the media is aware. If you partner up with someone or something in the community that is newsworthy be the first to let them know. It can be overwhelming when you are not familiar with these types of announcements so if needed you can hire a publicist to assist you.
My suggestion on press releases and the publicist is that if you do hire one have them sit down with you to show you what they are doing. Learn with them so if in the future you decide to take control of the publicity yourself you will be better able to create such items. Hiring professionals can be expensive but it is important to make sure things like that are done correctly so at least having someone advise you in the beginning may be a good idea.
Next is commenting on stories. Follow the news and watch for stories that fall into categories that would include your book. Submit comments to newspapers, online articles for television and radio stations. It is also a good idea to follow their social media pages to make commenting easier. The more often people see your name the more recognizable you will become for future events.
Going along with that is making sure you become a sort of expert on topics relating to your story. If you can comment often and offer insight others may not have thought of already you could become a go to for the reporters which only raises your visibility. Take every opportunity to promote yourself and your work so that you continue to grow your audience. Promotion is time consuming but one of the most important parts of being a writer.