Looking for an easy way to tighten up your writing? Eliminate phrases like which is, that is and who is. These are almost always needless words you can omit.
Avon Products, which is one of the world's largest direct marketing companies, hired its new CEO away from Johnson&Johnson.
The words which is are unnecessary. Delete them.
Avon Products, one of the world's largest direct marketing companies, hired its new CEO away from Johnson&Johnson.
Another example:
Pablo Picasso, who was an early innovator of the Cubism movement, was the 20th Century's most important painter.
Here, who was is the offending phrase. Nuke it.
Pablo Picasso, an early innovator of the Cubism movement, was the 20th Century's most important painter.
The corrected sentences have more cadence and more force. They'll keep your readers reading.