Some random tips:

Poke around the Accessibility settings. There’s lots of customization options hidden in there.

Learn the Shortcuts app. You can use it to create macros and save them on the Home Screen, in the share sheet, or as a voice command.

Customize the share sheet. Options are limited but there are some useful commands in there that are hidden by default. You may need to repeat customization with each files type (images get a different sheet from text, etc).

Set your AirDrop to “contacts only” or else you’ll get spam pushed to you when in public.

If you turn off wifi from the control centre it only disconnects. To turn off the radio completely you need to do it from Settings or switch to airplane mode.

You probably don’t need a calculator app, but if you do: pCalc.

Focus modes aren’t limited to “do not disturb”. You can have several with different home screens and different communication restrictions.

Apps that don’t have filesystem privileges can only access their own subfolder inside the “On My Phone” folder, so you sometimes need to move stuff into there manually. This is rare, but one common example is Minecraft worlds/texture packs.

If you dismissed the prompt to install Files, you can get it on the app store. Do it. Then install all the other cloud storage apps you use (Dropbox, etc), log in, then delete them from the Home Screen only and forget they exist. They’ll all be accessible in Files.

You can do a similar thing with the TV app, but personally I prefer separate apps on that front.