Short answer: on the first day, do the security settings and leave almost everything else alone. The settings that matter on day one are the ones that are painful to fix later. Notifications, home screen layout, and storage decisions get *better* if you make them after a week of real use — you will know which apps you actually care about.
Do these on day one (security, in this order)
These are the settings where "later" turns into "I wish I had done this first":
- Turn on Find My. During setup you are offered Find My iPhone. Say yes. It is the difference between a lost phone being recoverable and being gone. Settings → your name → Find My → Find My iPhone → Find My network on.
- Use a six-digit passcode, not four. Four digits is a million combinations and can be observed over a shoulder. Six is a million times more. Settings → Face ID & Passcode → Change Passcode → Passcode Options.
- Turn on two-factor authentication for your Apple Account. If you already have it on another Apple device, you are covered. If this is your first, set it up now — it is the single highest-value security step, and it protects the account that can wipe your devices.
- Check what the setup already agreed to. During setup, several screens ask for permissions on your behalf. Settings → Privacy & Security is where you see and change them.
Let these wait a week
Notifications. The setup flow invites you to configure notifications for every app, and at that point you have no idea which ones you want. Come back after a week: Settings → Notifications, and turn off the apps that have been interrupting you without earning it. See Notifications not arriving or delayed if something that should arrive does not.
Home screen layout and widgets. You will rearrange it anyway. Arranging it twice is wasted effort.
Storage and iCloud plans. Wait until you can see what you actually store. Most people buy more iCloud storage than they need on day one and still end up with a full phone a year later — the problem is usually what is stored, not the size of the plan. See iCloud vs computer backup for what each plan actually holds.
Battery care habits. Turn on Optimized Battery Charging during setup and then stop thinking about it. The habits that matter are simple: avoid heat, especially while charging. You do not need a charging ritual. See iPhone battery saving for which settings genuinely affect battery life — the honest answer is fewer than you would expect.
Popular setup advice that does not fit everyone
"Charge it for eight hours first." A leftover from nickel batteries. Lithium-ion cells do not need a forming charge, and hours at 100% is the thing that ages them. Use the phone.
"Install a battery or cleaning app." iOS does not let third-party apps manage other apps' memory or power. An app claiming to do so is either a repackaged shortcut to settings you already have, or a background process costing you the battery it claims to save.
"Turn off every background setting immediately." This is the most repeated and least effective advice. Most background activity is already throttled by the system, and turning it all off makes apps behave worse — mail arrives late, notifications are unreliable — for a gain you will not notice. If you want to reduce battery use, weak signal costs far more than background refresh.
"Set it all up now so you never have to think about it again." Settings do not stay put. Restoring from a backup, a major update, or replacing a device all change what is on. The settings worth locking down are the security ones; the rest are worth revisiting.
Before you erase the old phone
The most expensive setup mistake is wiping the old phone too early. Use the new one for a few days first — make a call, check that messages are arriving, confirm your banking and authenticator apps work — then erase the old one.
Two things cannot be recovered afterwards: authenticator codes that have no cloud sync, and chat history in apps that keep messages on their own servers. Both need to move from the old phone while it still works. See Moving to a new iPhone for the full list of what transfers and what never does.