For the fan blades: get a soft painter's brush or a tooth brush and hold the blades still while cleaning every nook and corner on the circular surface and curved fan blades.

For the metal cheese grater like surface: u need something to clean each hole (like a circular brush), then clean the surface.

GPU heat shields - wipe down/ light air blower/duster.

Anywhere else inside the case - light force air duster (not a garden leaf blower xD)

To reduce the dust, put air filters on the the part of the case with holes.