"Passive" does not refer to "past" tense. It refers to active vs. passive subjects and verbs. In literary analysis, always write the subject with an active (rather than passive) verb:

Example (passive):  The manager is described as enthusiastic.

Edit/Revision (active):  His other managers describe Steve as enthusiastic.

When you edit and revise, search for and revise "be" verbs (in this case "is") as a way to avoid passive voice - the actual active verb will always follow the "be" verb (in this case "describe"). Notice that editing and revising the passive voice demands a more specific subject (in this case, "his other managers." as well as identifying the manager "Steve." Active voice generates more specific analysis and content.

In addition to your New Century Handbook guidelines, these web sites may help you understand and correct passive voice.

Web Sites / Aides:

Plain Language Site

Princeton Writing Program   (requires Adobe Acrobat)