Writers should self-edittheir own work. That's a given.
Some writers approach the self-editing process haphazardly, putting little effort into the process. Those types of writers may rely heavily on a good copy or line editor to catch their mistakes.
Other writers self-edit a manuscript to death, striving to make every tiny detail perfect. An editor-turned-writer can often find the typos, grammar issues, sentence structure problems, etc.
However, even the perfectionists still need to get outside feedback. The truth is that no writers can view their own work objectively enough to catch all the mistakes, especially the bigger plot and character problems.
Writers become too enmeshed in their own story to be able to step back and view the whole thing from start to finish with a cold, critical eye. Writers gain that critical eye usually after they've stuck the manuscript in a drawer for several years. Then they're able to go back to it as if seeing it for the first time. (And usually they're amazed at the problems they find!)
Thus, no matter how skilled writers think they are in the self-editing department, at the very least every writer should get a big picture edit (known in the industry as a macro, substantial, or content edit, often lovingly referred to as rewrites).
A big picture edit pertains to all of the things that make for a well-told story like plotting, pacing, character development, themes, opening hooks, the closing, etc. These are the elements that win readers. Sure readers will get turned off by typos and poor sentence construction. But they can overlook some of the minor issues if the story grabs them and won't let go.
Thus I would venture to say that a content edit is THE most important type of edit, but in the industry is probably one of the hardest to get.
Where should writers seek this big-picture feedback?
It can come from a variety of sources. However, since this type of edit also tends to be the most subjective, a writer needs to weigh the feedback according to the source. I've listed them in order of degree of helpfulness (least through most) (although the order can vary depending upon many factors!):
1. Beta Readers: Beta readers can be anyone– family, friends, readers, fans, other writers, etc. The job of a beta reader is read the book with the "reader hat" on and not the "editor hat" and provide constructive criticism on what works and what doesn't. A writer can give beta readers some directive (issues to look for), even going as far as having a short questionnaire to fill out. Or the writer can simply ask for overall impressions. Beta readers should know they're NOT to edit or spend a lot of time making comments within the manuscript (if any!). They're simply reading.
2. Critique partners: Critique partners (or critique groups) are usually other writers at or about the same level of writing skill. These writers use a reciprocal exchange system for giving one another feedback on manuscripts. The exchange should contain overall impressions (similar to a beta reader's), but usually goes beyond that to include comments about writing techniques that need adjusting.
3. Mentors: Mentors are usually published authors who are above the skill level of the writer. Mentors can be found by entering contests and gleaning feedback through the contest judges. Mentors can also be found at writing conferences via paid critiques. Sometimes mentors can even be found through local writing chapters or an author who is also a good friend.
4. Agents: Although agents don't often have the time to give specific feedback on queries, sometimes they do. And when they offer advice, writers should listen carefully. Experienced agents sort through thousands of manuscripts and can usually spot what works and what doesn't. If a couple of agents are saying the same thing (i.e. that an opening doesn't grab them), then a writer should definitely take note of the issue.
5. For-hire editors: Over the past few years, many people have hung out a shingle offering editing services. However, before hiring someone, look at how long the editor has been in business, credentials, recommendations from current clients, and what levels of critiques the editor offers. The more intimately the editor knows your genre (and the more experienced), the more weight you'll be able to give their big picture feedback.
6. In-house editors: Editors who work for traditional publishers and have been in the publishing business for years are often the experts in their genre. They work closely with their marketing and sales teams and usually know what concepts, ideas, and issues sell better than others. They're often intimately in tune with what readers of a genre like and don't like (based on reader feedback and sales trends). Thus, in-house editors can offer an expertise to editing that is difficult to find elsewhere.
All of the above can be incredibly valuable methods for getting big-picture feedback. No matter which source, there is always some level of subjectivity (personal preferences) that come into play. Because of that, I never rush off to change anything (even when my in-house editors provide me feedback).
Even so, I always weigh each piece of advice carefully and thoughtfully. I lay aside my love-affair with my manuscript and try not to take the criticism personally. If I go into the content edit process with an eager desire to improve my story, then I'm better able to analyze the feedback and figure out what will help and what won't.
Usually if multiple people (at a variety of levels) are pointing out the same problem, then writers can rest assured that the issue needs to be addressed (and possibly changed).
How about YOU? Are you getting big picture feedback on your stories? If so, who's giving it to you?