You need to save your SLR from dust if you want to obtain consistent results. This is not an easy battle to win because dust finds different ways to get inside your camera body and stick to the sensor. This happens especially when the lens is being replaced. Sometimes it happens when the sensors get charged, and suck in dust.
The easiest way to avoid dust is to change the lens in a non-dusty place. You should never change your camera lens in a windy, dusty or sandy location. It is much better to change your lens inside a closed room before you leave for a shoot.
In case you decide to change the lens in the field then you should find a relatively sheltered location. You should also reduce the time the camera is kept open by keeping the replacement lens ready for a swap.
Always hold the camera facing down while changing the lens to avoid dust from entering from above. The mirror fixed inside your SLR offers protection to the sensor from dust to a large extent. The mirror/sensor chamber, which can accumulate dust, should therefore be kept clean to avoid dust from finding its way to the sensor.
Never clean the insides of your camera with compressed air stored inside an Aerosol can. The propellant in the Aerosol can sometimes sprays a liquid that quickly evaporates leaving a residue behind on the surface of the sensor resulting in malfunctioning of the sensor.
A blower brush that is available at most camera stores is a much better tool for cleaning the mirror chamber. When using the blower you should keep your camera tilted downwards. If you perform this procedure once a week you will greatly reduce the chances of the sensor developing dust related problems.
In emergency situations you can shoot with wide aperture openings. This reduces the camera’s depth of field and negatives the impact that dust may have on an image. However, this should not be made a practice. The dust, if it is allowed to accumulate on the sensor surface will lower its sensitivity.
Some lazy photographers prefer to remove dust with the help of an image editor. This can at best be called a short term solution. They must learn to keep their cameras free of dust if they want to use their digital SLRs fruitfully over long periods of time.