Well, one way is to let the author's unique perspective influence the themes and messages of the story. Another is to use real-life incidents from the author's life as inspiration for key moments. It's all about finding that connection between the author and the fictional world they create.
The key is to blend the author's input seamlessly. It could be through the setting, where the places the author knows well become the backdrop. Or it might be in the dialogue, where the author's style of communication shows. Just make sure it doesn't feel forced.
You can do it by having the author's thoughts and experiences shape the plot or characters. Maybe have a character based on the author in some way.