I use a small air compressor and a vacuum... and yes, you need to be careful with fan blades. I have ruined a fan once being careless and over spinning it. Works amazing for cleaning out the radiator though!!!
I find the best way to clean my computer's is a minor disassembly, a boars hair detail brush (usually sold for auto detailing) and a vacuum to pull in all the loosened dust. That or a very damp microfiber for large flat surfaces.
I use a rather large and powerful air compressor. I also use a pen, screwdriver or pipe tool (whichever I have closest at hand) to block the fans from spinning while assaulting them with hurricane force winds. It works great and works fast.
Just make sure you do it outside especially if you haven't done it in a while.
Before swapping my main system into a new case with a new PSU and putting my server in my old case I put the two computers into the car to drive them down to the shed where the compressor is. Even with being careful and taking my time I had both computers cleared of all dust with a few minutes of work on each computer. Neither one had been cleaned out in quite a while and had plenty of dust and dust bunnies. When I started swapping hardware around a couple of days later I didn't find a speck of dust or a single dust bunny anywhere in either case. Not even in the most remote and hidden corner.