Non-fiction, so I've found is much easier to get published by a traditional publisher than fiction. People seem to be really into "How to do things" or books based on facts. A friend of mine wrote a book on old railroad tracks and it was published. (He's a retired railroad engineer.)
I've discovered a few important aspects of writing non-fiction that helps a writer a great deal. (It has me anyway).
1. If you are an expert in the subject of your book, years of experience, that helps.
2. If you have a degree in the subject area, it's a huge help.
3. If you have ever lectured or taught the subject of your book, it's a big plus on your side.
4. If you've been previously published . . .well, at least they know you can write and that helps as well.
I decided a few years back to write a book on Wilderness Survival. I spent over 26 years in the military and of those, 12 were spent teaching survival to other military members as an instructor. Additionally, I have a degree in Search and Rescue, Survival Operations and over 40 year of hiking, camping, fishing, and hunting experience. I'm also a previously published author.
It only took me a little less than a year to find a traditional publisher and within another 8 months or so I was in print. The problem, in my opinion, is that new writers get a rush to be published. I've found once a publisher is found, it can be up to two years, depending on editing/proofing needs, cover design, and the printers schedule before the book is in print. I usually send a book in, file it as gone to the publishers, and then forget about it...but contact the publisher every four months or so for an update. Books are NOT published overnight.
Write your non-fiction on areas you know a great deal about, unless you do a great deal of real research and show your references. People who buy non-fiction want it written by folks who know what they write about and have the education or experience to do so.
Some non-fiction books, such as crafts or arts, should have a lot of photos showing the step-by-step processes. Others, like mine, don't require much in the way of graphic support, but graphics help in non-fiction books, or so I think.
All of this rambling is just one old man's opinion.