Before painting any surface, the first obvious step is to clean it thoroughly. A tennis court surface is no different. This step in the court resurfacing process can very well determine the longevity of the court surface.  Cleaning the court surface is just common sense. You are looking for debris, dirt, mildew, heavily oxidized, peeling, and/or loose paint.  Any substance that will prevent a strong bond between the old painted court surface and the new court coatings should be removed.  Dirt and debris are pretty obvious and can be removed from the court surface with a blower or vacumm.  It may be necessay to loosen the substance from the court with a broom or floor scraper before it can be blown away or vacummed.  

Mildew and algae are substances that are less apparent as problems, but are every bit as important to clean away prior to resurfacing your tennis court with patching or surfacing products.  While a pressure washer (minimum 1500 PSI rating) is the fastest most efficient method of cleaning, a garden hose, a couple of common household cleaning agents, and a stiff bristle broom will suffice.

If you do not have a pressure washer, mix a solution of chlorine bleach and water (2 parts water to 1 part bleach) in a five gallon bucket. Using a pair of rubber gloves, carefully dip a smaller bucket into the solution and then pour it onto an area that is covered with mildew. Immediately begin scrubbing the area with the push broom. Rubber boots are also in order when using this cleaning method. After scrubbing the area for a minute or so, rinse with clean water from your garden hose. If some mildew remains in the cleaned area, repeat this process, if the area is clean move on to the next spot. Continue until you have removed all of the mildew from the court surface. 

Most debris and dirt can be removed with a hand blower. Any areas where the dirt or debris seems to stick to the surface will need to be scrubbed with a push broom prior to blowing of the court..

To remove heavily oxidized or peeling paint, repeat these steps, with one exception, use a mild dish detergent in the bucket of water instead of bleach. For areas that still appear to have loose, peeling paint that do not come up using this method scrape the area with while wet and then repeat the cleaning process. Make sure that all of the old surface remaining has a good bond to the court. If you have access to a pressure washer, use it. It will take the place of all of these tools and will complete the cleaning in half the time.