How do I know if this filter will fit??

First off if you have a Injen System these filters are direct replacements, all you need to do is search for your original part number. Second you can use the measurements to make sure it will fit... the neck measurement refers to the area where you have the clamp to your intake pipe. Third and most important, you can CALL us to ask 866.Max.Speed ext.2

How do i know when to clean the air filter??

How often you need to clean your filter will depend on the air and road conditions in your area. Most filters require cleaning before the dirt build up gets as thick as the wire mesh. The usual interval is 30,000 - 40,000 miles depending on driving conditions. We recommend that you check your filter about once a year in normal usage and once every six months if you are located in a dirty environment. If you are running with a cold air intake we recommend checking the filter every 10,000-15,000. Using a Hydro-Shield will reduce service intervals

Is rotating my filter a good idea to get more longevity out of it??

This is actually recommended. Most vehicles have a particular area to draw air in from based on the filter surroundings and rotating the filter will keep it clean longer.

Should I hit the filter on the ground or use a brush against the screen to remove larger particles of debris??

No, this could damage the filter base or top and tear holes in the cotton gauze. Look if you need help give us a call 866.Max.Speed ext.2