They send you the directions with the cleaning kit. But just in case you lose it, here it is.
1. Remove your filter. Most of us will have cone or circular shaped filters.
2. Spray liberal amounts of cleaner on outside of filter. Coating entire exterior.
3. Allow cleaner to sit for 15-20 minutes to "marinate" and break down dirt and residue.
4. After time has elapsed, rinse with LOW pressure hose, in opposite direction of air flow (air moves from outside into filter). In other words: rinse from the inside of the filter so water flow out of the exterior. High pressure water will damage the filter.
5. After rinsing lavishly. Allow to ONLY air dry. Do not use anything to hasten the drying process (oven, hair dryer, etc) as this will damage the filter.
6. When completely dry, respray filter with K&N oil spray. This spray has a red dye that allows you to see what sections may need more oil. Allow oil to absorb and set. Repeat sprays as necessary to achieve that nice deep burgundy red that signifies you are fully oiled and dry.
7. Remount filter. Take this time to check all other connections to ensure their patency.
Note: with my cone filter, I find that oil and water (whichever is being applied in it's respective stage) settles onto the plastic base pieces. I air the drying of water, and the absortion or oil by rotating the filter so each drains back and forth (or up and down) the filter.
Do not take shortcuts. Play some video games or drink a beer in between the drying/setting phases. This will take some time so make sure you have nowhere to go.