You need to convey your meaning clearly in every sentence. In many instances basic verbs such as "to be" (is, was, are, were) can be replaced with more "advanced" verbs that make the sentence more interesting to read. Remember - verbs can make or break a text. You want your verbs to carry the reader's momentum forward, so use dynamic verbs that accurately capture the action you are trying to convey.
Ex: "The elephant was loud."
Better: "The elephant trumpeted loudly."
Both sentences have the same word count (four words) but the second sentence more animatedly conveys the action.