These should be avoided in writing. Using them creates passive voice rather than active, because they lack vigor and energy. Verb forms of “be” convey no action. This means the subject of the sentence receives the action instead of doing it. Avoid:

For example,
"A surge of power was responsible for the destruction of the pumps."
Or
"The pumps were destroyed by a surge of power."

Both of these sentences are passive voice because the pumps aren’t being destroyed in either sentence. The action has already happened. However, if the either sentence is rewritten to read, "A surge of power destroyed the pumps," it becomes active voice. The active word destroyed makes the writer’s point much more powerfully than the passive were destroyed.

Occasionally, a writer may need to use the passive voice instead of the active. For example,
"As harvest time approaches, tobacco plants are sprayed with a chemical to retard the growth of suckers."
Here, the passive voice is preferable because the writer wants to focus on the tobacco plants, not on the people spraying them.

Here is a hint for avoiding the "to be" verbs. Try to use the "-ed" verb form as opposed to the "-ing" form. For example, "I was walking through the forest" can be changed to, "I walked through the forest" thus eliminating the "to be" verb of "was."