Recommend Practices and Procedures for Android OS OTA Updates My questions: 


What are the recommended practices and procedures for Android OS OTA Updates.
Is it all right to download via mobile data instead of WiFi. 
How to get out of bootloops if the procedure screws up. 


Preferably answers without the use of root.

Why: My previous phone had never received OTA as it was old, and just the other day my phone, Samsung XCover3  (SM-G388F), got a notification saying it can update to Android Lollipop(5.1.1) from Kitkat (4.4.4).

P.s. are there any known bugs for this update on my phone(phone model as started above)
There is no problem with downloading via mobile data instead of WiFi. The main reason people prefer WiFi is because it is cheaper; WiFi is not generally not metered the way WiFi data is. The update file is downloaded in entirety before the actual update occurs, so the method you use does not affect whether the update succeeds or fails. 

Given the number and severity of vulnerabilities found in software, you generally want to update your Android OS whenever this is possible. Most phone manufacturers do not support phones for long; this period can be only 18 months from the time of release. 

You do not want your device battery to fail while performing an update. I recommend plugging in the charger to perform an update and not starting the update until your battery is sufficiently charged to expect the update can complete on battery alone anyway.