Vacuuming seems to be discouraged by most sources. It's said that the SMD adhesive can age and cause components to be sucked away, and that vacuum cleaners can generate static electricity, which is harmful to electronic components.
A more modern method is using compressed air, either from an electronic compressor with a moisture filter or from a can. However, cans often lack moisture filters, which means you could potentially blow moisture onto your electronics. But wouldn't you blow away the badly glued SMD parts?
Using a soft brush, such as a paintbrush, is also recommended. But some sources caution that the bristles can become charged with static electricity. Some forum users suggest grounding the brush to prevent this.
For heavy dirt, isopropyl alcohol (90% or higher) with cotton swabs is recommended. Of course, stay away from microfiber cloth on the inside, otherwise the static electricity will strike again.
And then there are the more extreme methods, like immersing the computer in oil or using special cleaning sprays designed for servers in data centers.
Heck... How do YOU clean the insides of your PC?
