TARGETS FOR REVISING
Rationale
Easy to Spot
Harder to Spot
Simple Sentence Syndrome

A writer can make the reader's task easier by providing the agent, i.e. by telling the reader who is doing what.
Example: A new protein was discovered. >>> 
-Scientists from Holland discovered a new protein.
-The undergraduate student discovered a new protein.
-The blind doctor discovered a new protein.

In general, if the "doer" of a given verb is generic "you" or "one", then passives are not an issue:

-Dog food can be found at most grocery stores. >>> UNPASSIVIZE >>> One can find dog food at most grocery stores.

However, if the agent of a passive verb is a specific entity, revise the sentence and tell readers who the agent is rather than making them infer as much.