I. It is not as easy as it sounds. It is not like pushing a button. The book publishing industry and its array of trained specialists from editorial to marketing have been doing it for hundreds of years. And not always very well, I am sad to say. But..what makes some people think they know what to do and even worse think they can do it better? Not only do I see this with self-publishers of printed books but with e-books as well. Too many mistakes being made and too much money thrown down the toilet because budding authors have the wrong attitude or information...or both. Take the time to find out how much it is going to cost and with what quality before you dive in. Get advice when you don't know where to start. Avoid joining the thousands of authors who in the past and even now produce such poor quality books and design that people to this day think of a self-published book as inferior to those done by traditional book publishers.
2. Watch out for misinformation. Take the time to find valid, high qualitiy sources, people who have been doing it a long time and can share that information in a reasonable manner. I know it is a chore to research and even more effort to satisfy yourself there is a "chemistry" between you and the source(s) of information. In the end it is worth the effort.
3.Don't sidestep the process and try to do what is needed 'on the cheap". Yes, you want to get good value. I agree that is uppermost. It has to be obtained while still remembering that quality is important. Sometimes this means delaying your goal to self-publish because you don't have the financial resources. Better to delay than push ahead an produce a bad book. or bad manuscript. or no marketing because the money is not available.
4.When you become a self-publisher and marketer you begin to wear many hats. Some of them may not be the right size for you. You have to recognize that in some cases you'd be better off to have a source or sources who can wear that hat on your behalf. Especially when this will give you quality in results and comfort you are dealing with the best you can get.
I would make the same case for those who prefer to go the route of an author hooking up with a traditional book publisher. There are many. Some are still operating in the ways of ten years ago. Others have or are embracing the new technologies and operating practices. You can easily guess who I would choose when wearing my hat as a Literary Agent.