1. install a custom rom as the stock rom can never be secure
2. enable full disk encryption if possible
3. delink the fde password that's also tied to the lockscreen password and set a new lockscreen passowrd or pin
4. set screen timeout to 15 seconds
5. install only foss apps from places like fdroid, etc
6. switch to a launcher that hides all your apps like µlauncher
7. install apps like wrongpinshutdown and duress to secure your lockscreen
once done your homescreen should look something like this
>apps
https://f-droid.org/en/packages/de.jrpie.android.launcher/
https://f-droid.org/en/packages/org.nuntius35.wrongpinshutdown/
https://f-droid.org/en/packages/me.lucky.duress/