If you want to be healthy, you need to be active.
If you want your writing to be healthy, the same rule applies.
The most effective writing is in active voice, where the subject performs the action.
Active voice is typically more direct, precise and interesting than passive voice, where the subject receives the action.
For example, the sentence “the ball was hit by Bill” is longer and weaker than the sentence “Bill hit the ball.”
How can you avoid passive voice? One easy way is to look for the word “by.” Many passive sentences have that preposition. The word following the “by” is typically the “doer.” Make the doer (in this case “Bill”) the subject of the sentence, change the verb accordingly and your passive sentence will become active.
Sometimes passive sentences require more rewriting, especially if the sentence begins with “there is,” “here are” or something similar.
To change such sentences, first drop out the “there” or similar word, and look for what is most important in the remaining words. You’ll probably be able to identify the subject fairly easily.
For example, “there is a lot of information on the web” could be transformed into “a great deal of information is available on the web” or “the web contains a lot of valuable information,” depending on whether you want to emphasize the “information” or the “web.”
Of course, passive voice is appropriate in some situations. It is generally used where the thing being described is more important than the doer, which is often true in scientific or technical reports, for example.
Overall, though, for clear, compelling (and healthy) prose, stay active!