Use the active voice. Avoid the passive voice.
In the active voice, the subject of the sentence does the action. In the passive voice, the subject of the sentence has the action done to it.
Lisa and Abdul climbed to the top of the Eiffel Tower, from where they sent the message.
The message was sent from the top of the Eiffel Tower by Lisa and Abdul.
Words like “was” and “by” may indicate that you’re writing in passive voice. Scan for these words and rework sentences where they appear. The Hemingway App does a pretty good job of spotting uses of the passive voice.
One exception is when you want to specifically emphasise the action over the subject. In some cases, this is fine.
Thousands of fish were killed by the oil spill.