This is a very common problem. The fan is a place we forget to clean. Out of sight, out of mind. I have a very simple solution to the problem. Use a pillowcase to wipe away the dust. Anything that falls will be caught in the pillowcase, safe to be shaken out outside. This will keep everything under the fan nice and clean.
This is what the fan looked like before the clean.
This is how I used the pillowcase. Simply put the case over the whole blade and the wipe away.
And TADA! Your fan is as good as new with no hint of that invading dust.