If you have people tell you the voice isn’t strong enough, your language is probably too generic.
Look for words that add more than one thing to the story.
Don’t say your Main Character (MC) “sat down.” Instead say they “flopped” or “settled” or “parked” or “perched.”
Flopped says they are relaxed and casual.
Settled could mean they are formal or that they plan to be there a while.
Parked means they are going to be there a while.
Perched means they could take off at any moment.
Those words do more than say the character sat. They tell us how they sat. That’s one way to give your writing a stronger voice.