Before applying the paint is necessary to prepare the area. You need to clean the surface from dust and all the damaged paint, you can use a spatula to help with this duty. This action will help you that the new coating of paint adheres better and last more.
More than having the correct technique, using the correct kind of paint will sure you succeed, there is a specific type of paint, this is designed exclusively to be used in the exterior, its properties make it UV resistant, waterproof and even it can resist fungus and humidity. You should know that the paint has to be totally dry before being in touch with water if is not will be ruined.
You can schedule this process to be done in summer or in a season with sunny days so your work will be done in perfect conditions.
Look around the property for leaks, many times these leaks are located around the windows, this could happen because maybe the sealing is worn or broken, you can easily solve this problem by applying silicone sealant, let it dry totally before handling the window.
Even though the paint has many properties to be resistant to certain conditions, you can improve this by applying fungicides before paint and also acrylic if is needed.
Take care of the place where you prepare the paint, is a good idea to use a piece of plastic in order to protect the floor, also cover all the surfaces that can be stained during the process, this kind of paint is very hard to remove after being applied.
Use appropriate clothes and shoes to perform this activity once the fabric is in touch with paint there is no way to remove the stain.
If you are working in a high place, take all the precautions to avoid accidents, security goes first always.
This is not an impossible job to do by yourself, but it has many precautions that must be taken and basic knowledge about techniques if you prefer you have always the possibility of hiring a professional.