Probably the easiest way to show you how to effectively rewrite the content from an existing article is to show you examples.
Example #1:
This is an excerpt from WiKiHow about combing your hair:
"Allow hair to air-dry before you brush it, to avoid damage. This can take a while, but it's better for the hair than blow-drying. Running your fingers through it periodically and fluffing the roots a little will speed the process."
Your paragraph might be rewritten like this:
• Before brushing your hair allow it to dry thoroughly to avoid damaging the follicles of the hair. This if much better than using a hair dryer which can dry out your hair. Try fluffing your hair occasionally as you comb by running your fingers through the strands.
This paragraph has the same meaning as the original with the important facts presented but reads very differently. You might even use a bulleted list of facts to make it even more original. This makes your content unique and it will make your buyer happy.
To be sure it passes for originality, after your article is rewritten you can check it with Copyscape.com. The cost for the pro membership is only $.05 per submission and it is much, much better than the free version so well worth the cost. Checking your articles with Copyscape will give you information you need should you have inadvertently copied another website entry. Your buyer will check your material with Copyscape before paying for the content so it is best to fix any problems before your buyer sees the material you submit. 
There are actually two ways to do a rewrite of content. You can read a paragraph, take the meaning represented and then put it in your own words by rephrasing and/or changing some key words. For instance our example begins with the word “allow”. You can look this up in the Thesaurus which is part of your Word software and find a good substitute to replace the word “allow”. If you are not familiar with Word you will go to “Review” in the tool bar section and then highlight the word “allow” and click on Thesaurus. If you do not have Word software you can use the free version, OpenOffice.org. In this you will go to “Tools” on the tool bar, scroll down to Language and then click on Thesaurus.Under the word “allow” in the Thesaurus search you will see a list under let (v.); let, permit, agree to, consent to, tolerate or under allocate (v.); allocate, set aside, make available, set a limit. Now you can see you have many great choices for the verb replacement of “allow” so all you need do is pick the one you feel is the best fit. Your rewrite sentence might then be “Before brushing your hair let it dry…” or you might say “Before brushing your hair permit it to dry…”
Occasionally you will run into a buyer who specifically requires that each sentence be rewritten separately. In this case you will just take the meaning of each sentence and rewrite it in the same way. The trick is to be sure the completed rewrite paragraph has a natural flow when you read it through.
When you are asked to rewrite a paragraph that contains a list of items either in a sentence form or from a numbered or bulleted list the trick is to rearrange the wording so it appears to be original.
Example #2:
This is a copy/paste from the website www.diabetes.org. It is written as a bulleted list.
"Type 1 Diabetes
• Frequent urination..
• Unusual thirst
• Extreme hunger
• Unusual weight loss
• Extreme fatigue and Irritability"
To make this original and unique you might write the list as a paragraph:
The symptoms for recognizing Type 1 Diabetes can be extreme hunger, urinating frequently, experiencing an excessive thirst, extreme irritability and fatigue and unexplained weight loss.
As you can see, the facts are present but are written in such a way that it becomes unique content for your article. This is all it takes to create valuable and unique content when rewriting articles for pay. Be sure to list your items in a different order than the original while still including pertinent content.