Each type of surface has its own unique requirements for preparation.
One of the most fundamental parts of any project which requires re-painting whether it be wood, concrete or steel is the effort put forth to establish a absolutely clean interface between the surface and coating to be applied. Contaminants such as salts, chemicals, mold, mildew, dirt or the previous coatings deteriorating all have the ability to interfere with the adhesion (bonding) of the coating to the substrate and the ability of new coatings to not break down and affect its performance.
Even the best quality paint jobs will fail if they applied to a poorly prepared substrate but preparing the substrate is only one of the things to doing a superior paint job. You must consider the types of tools or equipment you will need, weather conditions can change quickly and ruin your project, understanding fully the manufacturer’s application process and last knowing the right type of materials for the project you are doing.