Writing quality products is both an art and a science.  Unfortunately, with the advent of text messages, email, and the likes of Twitter, both the art and science of writing have fallen into disrepair.

The science of writing is the grammar.  Often times we can get away with bad grammar in our writing, and the message can still be sucessfully passed to the reader.  Sometimes, however, the lack of technical "correctness" can change the intended message entirely.  For example, the simple addition of a comma in the following (identical) sentences changes the meaning of the message in a significant way.

The greatest influences in my life are my sisters, Oprah Winfrey and Madonna.

The greatest influences in my life are my sisters, Oprah Winfrey, and Madonna.

In the first case, you have a very unusual set of two sisters, Oprah and Madonna.
In the second case, you have sisters (unknown number), and you have Oprah and Madonna as additional influences.

Copy editing can usually take care of many of these "scientific" errors.  While the science of writing is something we must pay attention to, I believe that the art of writing is the most important.  But how do you work on the "art" of writing?  I believe this is accomplished by reviewing a paper.  For me, the message is the most important part of why we write.