1/ Sand down the fan with 400grit wet & dry take off as much dust as pos you can use hot soapy water and then let it dry for a few hour`s.
2/ Plastic primer (white) show`s off the top coat better than grey,do light coat`s dont try and cover the fan in one go as you will get run`s and will need to start over again,2 coat`s of primer 15 mins between will do the job.
3/ Leave to dry overnite then sand down again,repeat step one.
4/ Top coat same as primer 2 to 3 light coat`s give about 15 mins between coat`s hold can about 30 cm away from fan.