You might be surprised that some of the most popular apps don't have the best privacy features, take a look at data sharing practices with Privacy Check.
Sharing your data is most common practice by apps. Many apps do this without telling you . Even uninstalled apps can still spy on, showing you adds in hopes that you will re-install.
For online searching and browsing, use DuckDuckGo or Firefox Focus and look into DNS for Mobile for a speed increase and privacy boost.
For those that really need top notch security, Orfox and TOR for Android are options.