Some models are notoriously difficult to keep clean. They have difficult to reach areas and vacuum cleaners and their brushes are either to weak to get the dust off or too strong and can damage the model.
Fortunately almost all models may be rinsed easily and safely with lukewarm water. As you can see on the picture above static grass is not harmed in the process.
Note that I don't recommend this approach to cardboard buildings or paper banners. They are usually very easy to clean however as they consist of flat planes.