1. Don't sync anything to icloud you wouldn't want the government being able to get it or generally want to keep private.
2. Go through privacy settings, especially location settings and check what you're allowing including system services, adjust as you feel comfortable while still meeting your needs.
3. Pay attention to what apps you're installing. Most profiling data is not sold by say Google directly off your phone but based off ad-networks incorporated in third party apps you install. The app store has a scorecard on all apps showing you how much if at all they profile and spy on you, make use of it, make wise choices, don't install bad apps.
4. Install a privacy respecting adblocker to help limit tracking while using the web browser
5. Limit permissions for apps. If you must use an app that has location tracking consider only allowing it while you're using the app, this may have implications for some extended functionality like updating while in the background or via Apple's little info tiles.
6. Disable siri or limit it, turn off "hey siri" mode in settings.
7. Enable lock-down mode (this is an extreme step and will result in some loss of functionality, Apple details the implications themselves so take a look at their page on it before doing so)
8. Disable radios such as bluetooth and wifi while outside your house to prevent any possibility of their use in tracking you. You can actually make a "Shortcut" using app of the same name from Apple to automate this anytime you leave home and I believe there are existing ones you can find if you search around.

Apple phones are fairly private as long as you don't use icloud for anything sensitive, apply common sense privacy settings, and pay attention to what apps you install and what permissions you give. Also don't send them crash or debugging data as that can contain personal info potentially so uncheck that option.