Paint the edges of the door first using the 1” paintbrush.
Next paint the faces of the door using the 4” paintbrush in sections in numerical order as shown in the diagram below.
Use a smooth wrist action that follows the grain of the door. As you complete each section, lay off the paint with a light upward stroke using the tip of the brush.
Don’t overload your brush with too much paint as this will encourage runs.
Check back over the door and remove any developing runs by brushing them out and laying off with an upward stroke.
Alternatively, if this method does not deliver a smooth enough finish, dilute your paint with a little water or white spirit, as appropriate, and use the 4” mini roller to apply the paint all over the door very quickly. To avoid the ‘orange peel’ look that this would otherwise create, immediately lay off with a clean 4” paintbrush.