I suggested that you should write your first draft without looking back. The first step in editing is to read the material again. During the first pass, you should be able to spot big things like plot holes, or flaws with the actual writing. I suggest doing as many passes as you can by yourself before handing it over to someone else. I went through The Check Out about 10 times before I let anyone else read it.
Once you've gotten everything fixed to your satisfaction...prepare to be shattered. That's really what editing is all about. It's a difficult pill to swallow, but a necessary one.
Choosing an editor for your project is an important decision. Yes, you can find a friend or spouse, but that can be very counterproductive. As a writer, you need to be constantly challenged. People that are close to you want to build you up. They are generally not going to point out flaws, or suggest that anything's wrong. If the only notes you get back from someone are "Wow, Great Job!" then, you need to find someone else.
There are a number of editors that you can hire. A simple Google search will pull up plenty. The issue is determining which ones are really going to get you the most for your money. When I was searching for editors, I quickly realized that they aren't cheap. The cost ranged anywhere from $1,500 to $3,000. Some editors offered the basic grammatical/spelling package, while others promised a more in depth review.
Most of the sites that I saw offered a free sample of their work, which is extremely helpful. They generally pick two pages at random, make notes, and send them back to you. You can go through and see exactly what they will offer you, and decide if its worth the cost.
Once you decide on an editor, and get their suggestions back, it's time to gut your work. This is probably the most difficult part of editing. You have spent so much time and effort perfecting your writing, just to have someone rip it to shreds. Some writers get really defensive at this stage; they rant about the notes and refuse to make changes. Again, this is very counterproductive.
At this point, you should read through the entire manuscript, and look at the notes. Most will probably be dead on. Some, however, you may not agree with. I would let someone else read through the pages and notes, and get their opinion, as well.
After you have gone through and made all the changes you can, fixed all the spelling mistakes, typos, punctuation, etc.....send it to someone else to read. Find someone who has never read it, and let them go through it. It's likely that there are things that have been missed, even up to this point. I know it sounds ridiculous, but this will save you money, time, and frustration.
The editing process is not a fast one. You can easily spend months going through the piece and making changes. Don't let it get you down. Instead, look at it as the chance to come up with new ideas, or polishing the package. While you are waiting for people to make notes, you can jump into the other areas of self publishing, like choosing a cover, distributor, etc.
Next session, we'll go through another important step in publishing: choosing a cover. Aside from editing, it's the most important decision you can make for your work.