The first step, apply some rubber gloves! This is a dirty job at the best of times, rubber gloves will keep your hands clean and prevent you from smelling like you work on an offshore oil rig.
To clean your filter first remove it from the bike and the housing cage, we recommend also covering your open filter duct with something to keep any debris from floating in there while your filter is being cleaned.
Following the correct procedure using the correct chemicals will ensure the filter is cleaned adequately with minimal damage to the foam. Using a chemical which is corrosive such as petrol can break down the glue which holds the filter together or begin to break down the foam itself, we recommend a purpose made dirt bike air filter cleaning product which are available in spray-on cans or a liquid which you pour into a container and submerge the filter in.