1 – Utilize an editor
The most common mistakes are minor, such as misspellings or incorrect use of punctuation. Other common errors are incorrect word use (their, they’re, there). A professional copyeditor is adept at noticing and correcting these kinds of mistakes. Do not make the mistake of relying solely upon a computerized spell-checker, which cannot tell the difference between “worse” and “worst” since they are both properly spelled words. Use an editor – a human one. Good self-publishing options will provide copyediting and other more advanced services. Be sure to ask your rep.
2 – Get a second (and third) set of eyes
Even if you do not wish to pay a professional, anyone who reviews your writing will find mistakes you invariably miss. Since you are overly familiar with your own work you are much more likely to miss obvious mistakes because your mind already knows what it is supposed to say, rather than what it actually says. When someone else reads your work, they have no preconceived notions about your writing. In addition to finding mistakes, other people may offer helpful suggestions to make your business writing stronger.
3 – Come back to it later
Do you wait long enough after writing something to begin editing it? Many writers edit their work as they write it. Not only does this slow down the creative process, it increases the chance that your mind will ignore blatant errors in deference to your intentions. Once your brain thinks a paragraph is free from errors, it tends to overlook any new errors that are introduced during the rewriting process. Put your writing away for several hours, days, or weeks and revisit it later. After some time away from your work, you will be more likely to read the words as they appear on the page, not as you envisioned them in your mind. The mind is error-free, the page is not.
4 – Read your material backwards
You are only familiar with your writing in one direction – forward. Reading your material backwards makes it seem entirely different and fools your mind into ignoring the intention and only concentrating on the reality. Furthermore, your critical view of the writing at its most technical level will not be corrupted by the flowing exposition you have massaged into sparkling prose. When you read your manuscript backwards, it becomes a collection of words. Without contextual meaning, the brain has nothing to focus upon other than the words themselves. Mistakes literally jump off the page.
5 – Read your material out loud
When you read words aloud, your brain must slow down and concentrate on the material. How fast can you read the following sentence? The quick brown fox jumped over the lazy dogs. Now how fast can you read it out loud? It takes at least twice as long, and those precious milliseconds sometimes make all the difference between a typo that is missed, and one that is caught and corrected.
As a popular Internet posting informed us in 2003, it deosn’t mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be in the rghit pclae. The rset can be a toatl mses and you can sitll raed it wtihuot any porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. But try raednig tihs out luod and see how far you get. An extra bonus for reading your material out loud is that you may discover stumbling blocks like awkward sentence structure and choppy dialogue.
Self Publishing Advisor 
With regards to your first point, even the supposedly biggest and best of authors – and publishers – fall foul of such minor errors. Look at page 79 of Martin Amis’ The Pregnant Widow, published by Jonathan Cape; a rogue apostrophe … (I blogged about it recently).
http://www.bitesizeedits.com/
A wonderful site where you upload your writing and you (and others) edit random sentences out of context allowing you to focus on grammer, spelling, etc.
@ Asrai: “A wonderful site where you upload your writing and you (and others) edit random sentences out of context allowing you to focus on grammer, spelling, etc.”
Did you mean ‘grammar’ for your third to last word?
Is “Mistakes literally jump off the page” a deliberate mistake? Because it figuratively jumps of the page as a misuse of the L-word. Criminal!
Paul Parry, Literally Tsar
For step 5 in your list, I simply use TinyPDF to ‘print’ my stories as PDF documents so I can use a screen reader to hear them out loud and more easily pick up errors than if I read them out loud myself. An interesting side effect of this is that it totally negates the necessity of step 3, because having my story read to me in mechanical U.S. tones is just like reading it afresh.