Once you've published your book, the best thing you can do for your career is to start writing the next one. But if you leave your non-fiction book alone to sell on its own, you're leaving money on the table. Any book of non-fiction is an attempt to teach people something, either knowledge or a skill, and reading is only one way that people learn. Reach parts of your audience you never thought you'd find by turning one book into six different ways to reach your readers. Your hardcover book is only the first step.
Hardcover might seem the natural form for your instructional volume, but there are readers who won't buy any book unless it's in digital form. Yes, it's harder to flip through pages on an ebook reader, but these fans are willing to make the sacrifice to get your work in the form they love.
Today's print on demand technology makes paperback sales a no-brainer. It doesn't take much more effort to put your book into paperback form, but those fans who always wait for the paperback (and you know they're out there) will be glad to finally be able to snap up your book.
If you've got a series of books in the same genre, turn them into a box set for extra income on the same words. Even if you've only got one book out on the topic, contact other authors in your niche and create an anthology of great non-fiction as a way to cross-promote each other. Box set buyers don't tend to be the same people as those who buy individual books, so there are no worries about cannibalizing your individual volume sales.
If your book tries to teach a task or skill, you've got readers who are working along with you, learning as they read. Make it easier for them by creating a work book to go along with your original volume. Pull out the most important details of each chapter and leave room on the page for readers to make their own notes. Sell it buy itself, or put the two books together into another handy box set.
Some people simply learn better by listening instead of reading. Take advantage of this fact by having your non-fiction book recorded and sold as an audiobook. It might be unusual to sell instructional audiobooks, but those fans who learn through auditory stimulus will thank you.
Turn your book into a series of instructional videos. Teach a skill from each chapter by doing it in front of the camera. If your book is historical or biographical, record yourself reading a chapter at a time and turn it into a weekly podcast. Charge for the series or put them up on YouTube and make money from advertising on the clips.
Keep the Faith and May the Force be with You!