First off, in terms of cleaning your fan - make sure the power is off! It's important you don't get an electrical shock when you're doing this. That means not only turning the fan off but also turning off the breaker in your home. Make sure the power is off before starting.
Once that is taken care of, the next step is to use a damp cloth and simply wipe it along the edges of the fan blades. This will remove all the dust and anything that has accumulated on the blades. Make sure the cloth is lint free. Don't use any cleaning agents on your fan - this can ruin the fan.
Another thing you can do is check the manual that came with your fan, in terms of the cleaning instructions. If you have the original manual that came with your fan, that is always useful. If you do not, you can try searching online for the manual, PDF, or user's guide. Sometimes the manufacturer website will have the user's manual that you can download in a PDF file format.