i give everything a good dusting every few months. as dust = more heat and more heat = more wear on parts which = higher likelihood of failure. there really isn't much else you can do other then maybe work on ways to keep your rigs cooler.

replace filters as needed (commonly 3 months or so but last summer was more like every other WEEK due to the high smoke levels).
Dust as I notice buildups.
Monitor temps on the GPUs and get proactive when I see one getting too high - but that's more commonly my Gigabyte cards having fans wear out and die than all other reasons combined (DON'T buy non-AORUS Gigabyte cards, the fans are JUNK).
 
 

You also need to check regularly how the pool is working and how often it experiences connection or stratum errors. Testing the latest driver and bios releases is another thing. Also sometimes drivers will stop functioning correctly and much time is needed for troubleshooting.

Mostly dusting as others have said and driver updates. I also unplug my cable modem every few months for a few minutes. If it's always on then the updates the cable company makes you are not getting probably won't do that much but if you are turning things off anyway to dust might as well give the modem attention. Also keep in mind networking equipment needs attention and dusting. 

Use a 2200 3m filter on your AC, use canned air at least once a week on cards and MOBO.  Keep pets away.  Spend a little now save a ton later.

any good exterior filters out there for cases you can just add on

I use a can of compressed air on it when I see some buildup. That ends up being a quick spray about once every two weeks.

yea, if you are doing a lot of dusting an electric option is MUCH better than a can. because once the can starts to cool down you lose pressure and have to wait a while for it to get to room temps again.

This is what I use to Filter the Coolant.
I filter it twice changing the Coffee Filters, I double the Filters that is.

EchofoxtrotFTW
any good exterior filters out there for cases you can just add on

 
Demciflex  http://www.performance-pcs.com/demciflex
 
to make your own with small magnets to hold it on  MDY-FF-PVC-M-30 from company in link above
 

 
Premium Ultra Thin 0.17mm PVC Case/Fan Dust Filter Material - 30cm x 29.5 cm
 
I just bought mine, there is a current coupon code to save 10% to 12% depending on size of order --> check my link in Hot Deals
 
Performance PCS usually beats Amazon prices, though site can be clunky & shipping not cheap - I've had good service

@bcavnaugh
What brand & finish on your Q-disconnects - what is the average life before the have issues in your experience