At least once a year you should bring in your DSLR to have the imaging sensor cleaned.
General cleaning & maintenance includes:
The technician starts by checking the functions of the camera and attached lens. Before we start cleaning, we take a photo of the sensor to see where the dust and debris on the sensor is (image taken at f/22).
Then the cleaning process starts by externally cleaning the camera body and lens, this way we don’t introduce any new dust or debris. We then clean the inside of the mirror box, which consists of the mirror box, mirror, focusing screen and sensor.