1. Turn Siri into an English butler. Ask him to "Call Josh," and he'll respond, "Ringing Josh." His confused responses to your silly questions seem downright charming. General --> Siri --> Language --> ENGLISH (UNITED KINGDOM).
2. A special sub-tip: Siri can now read you any bit of text you select. Accessibility --> Speak Selection --> (On), Voices --> Select. And choose the speed, too. Then, when you select text, you move the black bar to the left until you see the "Speak" selection.
3. Want a more Android-like interface? Though it's possible to adjust the size of the default font (Accessibility --> Larger Type), you can also invert the colors entirely, turning your white pastel experience into a more clear, machine-like display. (Accessibility --> Invert Colors.)
4. Save your passwords and credit card numbers in Safari. This is quite convenient, and saves you from having to re-enter your credit card number inside the window of the mobile version of a website. Settings --> Safari --> Passwords and Autofill, Saved Credit Cards — enter in your card, and then toggle Credit Cards to on. Of course, you'll want to make sure you're reasonably confident that your device won't be stolen, but Safari won't show you the card you entered, so even if someone manages to access your phone, you should be okay.
5. Save battery by reducing automatic system service updating. This requires a bit of hunting. Settings --> Privacy --> Location Services — scroll ALL the way down, past all of yours apps — to System Services, and you'll see a plethora of toggles corresponding to different ways that your phone can communicate with cell towers and other devices. Some of them, like Diagnostics and Usage, tend to run constantly in the background; others run only when you start up an app. Disable a few of them, and your battery life should last a little bit longer.
6. The new Control Center can be useful, but it can also be annoying if you're playing a game. It's easy to disable it. Just go to Settings --> Control Center --> and hit the "Access within apps" toggle.