Before two decades ago, when any author used to write a book, they used to think that they would maximize their sales by writing for everyone. One piece of content or one book was made so generic that everyone could relate to it. In this way, the publishers and the author were under the impression that they would maximize their sales.
But what they did not understand is that one book or article or video or podcast is not made for everyone. If you are a teenager living in a metropolitan city you would not like reading something which a housewife from a rural area would like to read. People are different and so are their choices.
Publishers understood that if the description of the book does not fit the perception of one community, then they should not focus on it. They should move on and try to promote the book within the category of people who like it.
Therefore you might have noticed that Sci-Fi books are meant to increase curiosity among teenagers and nerds. So they focus on them only. They do marketing tactics that will attract these people. They go to Comic Con or collaborate with a young YouTuber. You will never see them going to a daily soap and promoting it.
Similarly as a writer it is extremely important to understand your audience. Before writing a book, sit down and note down the demographic of people who would be interested in your book. Categorise them according to their age, profession, choices, favourite pop culture icons, et cetera. In this way, you can use more of these elements in your book to make it sound more interesting to your readers. If they use social media, try to observe the accounts that they follow. In this way, you will be able to categorise your audience more vividly.
Try to communicate with them through other channels. A few easy Google searches will take you to online communities, blogs, and networks where your target audience is already talking about and sharing the information and doing promotional activities. Try to look for blogs and articles that are within your genre.
You can also look at the author websites of the established and top-selling book authors to see what their blogs are talking about and who is commenting on it. You can also network with them by engaging in guest posting and guest hosting activities to gain exposure to other audiences.
In the end, keep in mind that you are writing for a specific group of people and not for everyone out there. If it were for everyone, it would end up being for no one. Adapt your content to address the main concerns of your audience. Also keep in mind that the narration or voice of your content or book also matters to your audience. If you have already read some book in that genre, then you have some idea of it. If not then try writing accordingly.
Remember your target audience is your end goal.