My experience is limited in most of these areas, but I definitely agree with "cut no corners". Self-publishing has a dubious reputation precisely because people tend to cut corners. "Don't judge a book by its cover" is a dangerous line of thinking, because half the time, the book cover is the first thing people will notice about your book, and they will definitely judge your book by it. I think getting a profesionally made cover is perhaps the most important, singular step to take, if you want people to take your self-published book seriously.
Second to that, which you also mention, Jo, editing and layout. A book with spelling or grammar errors will turn people off from the first page. Poor layout that makes reading annoyed can do the same. I have no knowledge of layout myself, but I had a friend who does layouts for books, and she gave me wonderful advice that improved the reader-friendliness of my book immensely. If you don't have friends to count on, find online sources. A good cover gets people to open your book, good editing and layout helps them read past first page, and a good story makes them read to the end.
