UKC

I've been waiting to get a new mobile phone and move provider.
I have had a Samsung Galaxy for about 8 years on an old EE/T-mobile SIM-only package and it's time to change phone and provider.  Just seen the phone I want (Google Pixel 4) drop in price (been waiting for about 5 months) so pounced, and have also ordered a giffgaff SIM.

So now I have the excitement of transfering settings, apps, data, contacts etc between handsets and also migrating my existing number from EE to giffgaff.

Any tips, gotchas, useful "do this before you migrate" ideas before I tumble down a well-trodden path of to-be-avoided pitfalls.
Any useful idiot-proof (for the technologically challenged) guides on the steps to take?

TIA
YL

They're both Android phones so I believe that as soon as you log in to Google on the Pixel it will pick up a fair amount of that stuff from the Google cloud automatically.  It should certainly get your contacts, and I think a fair few settings such as wifi networks (though not things like developer mode, which you have to enable yourself).  I think it may also pick up the apps you had on the Samsung from the Play Store for you, though I may be mistaken about that one.  Any files you had on Google Drive will also be accessible on the Pixel.

Any Samsung-specific functionality on the Galaxy likely won't be transferred automatically to the Pixel.

I recently switched from a Samsung Galaxy to a Moto G7 power. Just make sure your contacts are backed up to your google account and not on the sim.

Once you log onto your google account on the new phone it's dead easy to download them. 

I don't think theres a single step to download all your apps at once, but google play  remembers all your purchased apps etc.

Changing phones is a good excuse to clear out old apps and update passwords as you download and log into your various apps and accounts.