Well, actually I don't....and that is often a major problem.
I can't stress enough how important it is to PROOF your manuscript before you submit. The hard part is that being so close to the work, it is easy to miss the simple errors like turned quotes or two periods or misspelled words that look similar to the original word, ie: 'maent' instead of 'meant'
Your eyes see what you want them to see because you are focused on the more important things like POV and structure. BUT, the editor's eyes are not. Unfortunately, we pick up on the little things.
And just to be clear, I'm not talking about the occasional incident; we more than understand this can happen. I'm talking about the multiple proofing misses that keep popping up where at least half should have been noticed if a solid proofing had been done--this is a case of NOT the more the merrier.
A few tricks of the trade:
a) Have someone else read the story for you, giving them instructions to watch out for the simple fixes needed;
b) Change the font--a different font can trick your eyes to seeing things in a different light;
c) Read the story backwards--this takes the focus off the sequence and makes you look at each word and symbol separately;
d) Read the story out loud. Yes, the simple action of verbalizing the story can make a huge difference because your sensory perception is to visualize the word as well as pronounce it. This is also good for listening for natural dialogue (when contractions should be used for instance) and flow of sentence structure. If you stumble over words so will the editor, or if the dialogue sounds robotic, it will sound just as metalic to the editor.
So, give an editor PROOF that you are doing your homework and take a bit of extra time to make sure your best--and the right--words shine!