Five Things You Must Do:
1) Contact your publisher so you know exactly what they are going to be doing for you in regards to promotional materials, book signings, advertising, etc...
2) Order business cards that preferably show your book's cover, include the title, your name and contact information like an email address/web site/blog site. Carry these with you wherever you go and exchange cards with every new contact.
3) Join one online social networking site. This can be a general site like Facebook or MySpace or be specific to your area of interest (i.e. Mormon moms, thrifty shoppers, outdoor enthusiasts...)
4) Host a webpage or a blog. How often you update it can be up to you. Even a place where general information is available is a start. Then, try and link your site to as many other sites where people who might be interested in your book go. Once you're linked, the hard part's over and you can put your focus on other things.
5) When your book's release date grows near, contact local newspapers and volunteer to do an interview or send out your own press releases. Don't forget other venues like alumni magazines, church and civic groups for a little free advertising as well. If you have connections--use them!
Five Things You Could Do:
1) Visit local bookstores the week your book is released. Meet the managers and staff and, if possible, bring a little treat or promotional item that will remind them about your book. Offer to sign the books they have on hand. Have bookmarks you can leave for customers. For bookstores out of your area, consider sending fliers or postcards announcing the release of your book and thanking them for their support.
2) Find the names of reviewers related to your book's genre and ask your publisher if they'd send out ARCs (advanced reading copies) or electronic files to those reviewers at least 1-2 months before your release date.
3) Find out about local book fairs, writer's conventions or other venues where you could arrange a book signing. Think of your target audience and be creative. (i.e. grocery stores, athletic shops, bakeries, organic markets, cultural celebrations)
4) Arrange for public speaking situations where you can be "expert" on a given subject.
5) Enlist the help of family and friends. You don't have to do it all yourself!