Spread a drop cloth under the area of the porch you'll be working on first. Run a paint scraper across the painted area of the porch with a back and forth motion to remove peeling and loose chips of paint. Continue until you have removed the peeing paint from the porch.
Sand the exposed paint surfaces of the porch with a sheet of fine-grain sandpaper. You can wrap the sandpaper around a block to make the job easier on the porch's flat surfaces.
Rinse the painted surfaces of the porch with water from a garden hose and allow it to dry.
Prepare a mild solution of dish soap and water -- about 1 tsp. of soap per gallon of water. Wash the painted surfaces of the porch using a sponge and the solution. Rinse with water from the garden hose and let dry.
Apply a coat of primer to the painted surfaces of the porch with a paintbrush. Let the primer dry and then paint the porch the desired color. Use primer and paint designed for outdoor use.