1) Blog and Social Media Links
Create a blog or website well in advance of your book launch, and keep your followers informed of your progress. Remember to include information on your blog/website and social media links at the end of your book.
Ensure your book is of the very best quality, by enlisting a professional editor and book cover designer. It will pay dividends.
3) Keywords and Categories
Choose your categories and keywords for online retailers carefully. Try to find categories that have smaller numbers of books to boost your rankings. Keep a close eye on your progress, and tweak as necessary.
Keep your prices in line with your competitors. Readers will not buy your book if you charge too much. Regular discounted offers will increase sales.
5) Read and Review Books
Read and review other author's books, and post to your blog/website, social media, BookBub and Goodreads...
It will come back to you in many ways.