Its important to know which side is the dirty side and which is the clean side.
Always blow out the filter from the clean side never from the dirty side. this would push the dirt in further
Before fitting the filter wipe out the housing especially the sealing area
Some manufacturers recommend not blowing out the filter. These usually have an air filter restriction guage on them and the filter is replaced when the guage shows its a certain amount blocked
One way to assess if your air filter needs replacing is to put a light on one side and see how much light shines through. Doing this with a new filter will give you a good reference point