There are lots of recovery and prevention options and I would like to put them all under one topic. (I'll also be making a video on this)
Color calculators:
Recovery :

turn it off and on again
RAM reset
Leave the battery out for 10 minutes
OS reinstall (press and hold [2nd]+[del] then press the reset button)

Prevention :

don't install sketchy ASM programs.
For CE only:

• Use Cesium and its backup options
  
• Use BLAST virus scanner (for the very, VERY paranoid )
  For CSE only:
  
• Archive all your programs and install DoorsCSE

Monochrome:
Recovery :

turn it off and on again
RAM reset
Take out the batteries and the backup battery for 10 minutes
Clean out the I/O port (the thing that looks like a mini headphone jack)
Reinstall the OS (press and hold [del] then press the reset button)
For a garbled screen:
Repair the ribbon cable topic and video

prevention :

Archive all your programs and install DoorsCS 7

Diagnostics:

Self Test (thanks to mateo for link)

That is all I know off the top of my head! Please fill in any missing information and I'll edit this post to accommodate for it! (I'll give credit too)

Well for the CSE, DoorsCSE does have some amount of redundancy. If a program is archived, Doors wil keep it in ROM during execution, which prevents it from being deleted should an asm program cause a ram reset. Thus, keeping all your programs in archive with DoorsCSE should prevent them from getting accidentally erased. (without losing the ability to run them of course)

By recovery prevention, do you mean ways to find whats wrong and / or fixing it? If so, I think it is worth it to mention the self test.

The CE Self Test
This tool checks the internals of your CE to verify they are working properly. To access the self test, press [mode], [alpha], and [s]. You then press [enter] and [enter] to start the test. You can choose a specific area to test or test all areas. You can read more about how to use this here and TheLastMillennial has a comprehensive video on this there.

Please post below if this is available on monochrome cals and I will edit this post.

You posted diagnostics, not recovery or prevention per se.
However you have a good point, I should inform people about self test. It may be able to tell you if something bad could happen. I.e. A RAM or FLASH defect/failure.(Self test is available on all TI84 type calculators)