In an edition of Editors on Editing from Grove Press in New York he summarized a lifetime of editing experience. The book also contains a large number of essays by other American editors on different editing topics.
Isn't editing exactly the thing that an author would leave out if he's walking the self-publishing way? It can be, but it's also possible to hire and work with an editor - perhaps a freelance editor who has time to go through your manuscript and discuss it with you. Some people would highly recommend it. Gross was one. It can in fact be the first contact you make with the publishing industry and (besides the help with the fact checking and revisions) may turn out to be a good contact in the self-publishing world.
Ask the editor if he has self-published a book himself or worked with other self-publishing authors. There are many examples of writers (at least in the English-speaking world) who both self-publish books and edit books and manuscripts for other writers. There are also examples of writers who swap manuscripts with each other in order to help each other out.
Editors are as self-conscious about their profession as writers are. They are proud of their skills. You may want to find one that's happy to help you or one that has skills in your book's area. It's certainly different to work with someone who has only general skills on the topic that your book is about - or one who knows the area well. The interesting thing is that both the one with general knowledge and the one who knows a lot could add much to your book and your self-publishing experience. Because, the most important thing could in fact turn out to be how well they know the market and the publishing industry - and what you can learn from the editor.
The main problems when you want to self-publish is to see your book through the readers' eyes. Isn't it? That's exactly where a professional editor can help. Another thing is how to organize the book (chapter by chapter), put a tile on it, have it printed (or should it be printed at all in this era of digital tools such as e-readers), distributed and sold. How will you market the book? How will you price it and in what way will you sell it? Self-publishing on Amazon Kindle is a trendy thing to do at least in the English-speaking world. And Kindle is a e-reading tool that many both readers and writers like.
But, how will you find one? Many editors advertise their services on the Internet. You can also check if there's a writer's conference to go to in the city where you live and make your first contacts there. Perhaps you can ask at your local library if they know of a writers' conference.
Gross - who summarized 30 years of experiences - wrote that editors and authors can work together symbiotically. When he first started his editing career many agents complained that editors edited too much. Today, he wrote, editors care and know enough about shaping the theme and content of a book to make it the best possible expression of the writer's intent and art.
There are many creative, technical and empowering ways in which an editor can work with a writer - published or a beginner.