For new weatherboard seal the surface with an acrylic primer undercoat, such as Resene Quick Dry and apply two coats of an acrylic paint. Consider the sheen level used, most paint is manufactured in a range of sheen levels which generally include Gloss, Semi Gloss and Low Sheen. A popular product choice is often Resene Sonyx Semi-Gloss Acrylic designed to withstand New Zealand weather conditions this paint is tough durable and easy to maintain. Paint with a higher gloss level is more durable and easier to clean whilst a lower sheen will hide imperfections.
For older weatherboard buildings check for any boards that might need replacing or may need treating with a timber preservative such as Resene Timberlock. Cedar weatherboards and some older wood surfaces require an oil based wood primer, this will block any oils bleeding through the top coat and assist with adhesion. Lower sheen levels such as a Resene Sonyx Semi Gloss or Resene Lumbersider Low Sheen tend to suit older weatherboards unless the weatherboards are in exceptional condition.
Painting older weatherboards can be problematic and is often most successful when the original paint coatings are scraped and stripped back. If this not possible ensure the colour of the new top coat is as close to the original colour as possible, this can avoid bubbling and blistering through heat absorption.