First of all, if your application is rejected, there is no problem, it will be better for you to see your mistakes and correct them in order to learn.
As far as I have experienced, you should provide valid information in the privacy policy and data security steps. Because if these are invalid, your application may be removed later even if it is published at the beginning.
You should create a test user for your application and provide this user information to Google Play. (If your application has a login)
There should be no sensitive permissions in your application. If there will be, you should explain them properly. You can read for sensitive permissions ---> https://support.google.com/googleplay/android-developer/answer/9888170?hl=en
When obtaining permission from the user in your application, you should write a valid explanation that informs the user in detail.
You should test your application on various screens.
Finally, do not forget to give internet permission.
You can also get help from here ->>> https://docs.flutter.dev/deployment/android#publish-to-the-google-play-store