Open Settings
Tap your name at the top
Tap iCloud
Turn off the apps you do not want syncing with iCloud
Scroll down and tap iCloud Backup
Turn off iCloud Backup
Return to the main Apple ID screen
Tap Find My
Turn off Find My iPhone
Enter your Apple ID password if prompted
Tap Sign Out
Choose whether to keep a copy of your data on the device
Confirm Sign Out
If needed, go to Settings > [your name] > Media & Purchases
Tap Sign Out there as well
On a Mac, open System Settings
Click your Apple ID
Select iCloud
Turn off iCloud features you do not want
Click Sign Out to deactivate iCloud on the Mac