Editing is where you make sure everything reads smoothly.

Check that you have done each of these things:

Parts of Speech:

Did I use a consistent verb tense (e.g. past or present) throughout my writing?

Do my singular subjects have singular verbs and my plural subjects have plural verbs?

Did I use the best words in my writing?

Sentences

Do all my sentences express complete thought?

Have I eliminated run-on sentences from my writing?

Have I eliminated short, choppy sentences from my writing?

Have I eliminated long, rambling sentences from my writing?

Did I use a variety of words and phrases to start my sentences?

Have I eliminated words that don't add meaning to my sentences?

After you have edited your product user manual, read it aloud at least once.  Let your ear tell you what sounds awkward or ungrammatical.

I have read my user manual aloud at least once.