First a couple checks. Have you set the automatic sensor cleaning options from the setup menu? Page 210 and 211 in the manual. This will generally get rid of most of the dust. I doubt you have sand. If you do then you put the camera some place where you shouldn't have.
Use a bulb blower like the Giottos. This normally takes care of 99% of the spots on the sensors filter. It will not clean the sensor if the spots are caused by oil drops.
If everything above fails, then the sensor filter will need a wet cleaning. In the last 10 years or so I've owned maybe 10 digital cameras and only had to wet clean the sensor filter once. And that was my fault. A drop of water got on the sensor.
If you wet clean I would recommend a pro do it. And don't buy a generic cleaning kit you might see advertised by an on-line store. They are a rip off. You only need the Giottos bulb.