Before finishing, repair all nail holes and surface irregularities. All surfaces should be clean and caulking should be in good condition. Seasoned cypress siding should be finished promptly at the time of installation to protect against moisture absorption, discoloration from rain, and mildew. However under no circumstance should siding be finished when it is wet.
Use a high-quality primer compatible with the paint being used - most paints will require an oil-based alkyd primer. High quality/100% resin acrylic/latex apints are recommended. Certain paints contain water-sensitive polymers and/or surfactants that might absorb moisture, causing the siding to swell or creating an environment suitable for biological degradation. These additives are present in a variety of paints, at difference price levels, and their presence is not necessarily reflected on the label. The only safe approach is to use a paint specifically recommended by a paint manufacturer for use on exterior wood siding. Light-colored finishes reflect heat more than dark colors and reduce the possibility of shrinking, checking, warping, and loosening of nails.
Always follow the primer and paint manufacturer's recommendations. Priming all sides and edges of wood siding provides superior performance over all types of sheathing. After the prime coat has dried, apply two coats of high-quality paint to all exposed surfaces and edges. Brush application is recommended because it provides a more uniform coverage. Time of day, temperature, dew, fog and rain influence the quality of the paint job. Follow paint manufacturer's recommendations in regard to these factors.