My Studio and Home Lab collects a LOT of dust. My house was built in like the early early 1900s so has a lot of stone walls and stone foundation that has deteriorated. Not quite "dirt floor" status, but definitely "dust floor". So I clean my rigs/servers rather frequently due to build up.
I have a small air compressor that I use to blast air through all the fans, cracks, n crevasses. After that I do the same as
@Condobloke and wipe everything down with alcohol swabs.
I like to change my thermal paste once a year unless thermal readings indicate it needs it sooner (It's actually never indicated there's an issue due to my insistence on keeping it "fresh"). I figure if I'm yanking components for cleaning, at some point I might as well repaste just to be 100% certain she's good to go.
As for the dusting, I just keep an eye on the front panels filter and once it starts looking like a jack rabbit I figure it's time to clean it lol. Server's the same way, but I just keep an eye on the rack's top fan and once it's turned grey I typically clean it up.
I've heard a lot of old timers claim there's no point in cleaning them, that it doesn't "make that much difference"; but I've always been of the belief that at the bare minimum one should keep their fans clean to ensure longevity and low resistance.
It's mind boggling to me some of these dudes that have like 6'' of dust and cobwebs built up in their case. I mean, if it works it works, but it'll work longer and better if you take care of it lol