When you begin eradicating weak and passive verbs, you'll find that unruly prepositional phrases fall by the wayside as well.  Read the following sentence, a prepositional wasteland: 

The costumes for the school play were designed on Friday by the students from Mrs. Jacob's fourth period art class.

This sentence never ends.  The author added so many prepositional phrases that we the readers lose sight of the sentence's direction and meaning.  Try:

On Friday, Mrs. Jacob's fourth period art class designed the costumes for the school play. 

Not only has the sentence lost five unnecessary words, we get the details about the subjects and the time period (Friday) up at the front of the sentence.  We're not so weary by the time we find out the purpose of the action.

As you make your way through another red-lined sentence, and another, and through a paragraph, you'll find that sometimes a "to be" ought to be.  The forms of "to be" work well when you want to link a subject to a noun that clearly renames it or to an adjective that describes it.  Trying to meddle with a "to be" verb with one of these functions might just alter the meaning of your sentence or add an action when one truly doesn't exist.  For example:

Advertising is legalized lying.

Any attempt at getting rid of the "is" in this sentence makes for a wordy, confusing statement.  So don't be too rigid about eliminating every single "to be" verb in sight, but do examine your motives in using the verbs you choose. A conscious decision to use a "to be" verb may be just what you need.

This passive voice elimination process seems tedious, and it truly is the first time you try it, but you'll begin to notice patterns in your own writing and ways to fix them. Soon, you can avoid the red pen therapy because you'll begin writing more actively in your rough drafts.  You'll think in terms of verbs instead of nouns, and your writing will gain intensity and verve.

It takes work and lots of red ink, but abolishing passive and weak voice can only bring rewards.  Good luck, and, hey, maybe I'll see you sometime at the office supply store...in the red pen aisle.