With these garage doors the center panels have vertical planks as you can see in the next photo. I do a lot of taping off when I paint a garage door. That is so when I make a paint stroke to simulate the grain pattern I have no start and stop marks. You can see how I have taped off the panels to paint in the vertical grain on the planks and the space between the individual panels.
When the vertical panels are complete I paint the space between the row of panels with a horizontal grain, that space is indicated by the white arrow in the next photo. You can see how I have taped off for that.
When I tape off to paint the horizontal grain you can see a close up next of how that goes. The green arrow indicates the beveled part of the center panel that gets a horizontal grain. The red arrow shows how I leave just about sixteenth of an inch from the vertical grain painting exposed. That way when I paint in the horizontal grain the brush will cover over that thin area and leave no blank area not painted. The white arrows show some bleed under from painting the vertical planks. It is minimal and when I paint in the horizontal grain in those areas you never see it.
Next photo shows the horizontal grain once painted on, indicated by the green arrows.
Once the center garage door panels are painted with a vertical wood grain I then go around the perimeter of the panel on the beveled part and paint in some dark lines in the grooves that are there. On this garage door there are three grooves I painted darker indicated by the arrows. I also (blue arrow) painted in the groove between the vertical planks with a dark stroke.
You might be able to see what I am talking about better by looking at the next two photos of the completed garage door painted to look like wood.
The next three photos are of the finished garage doors. Painting your garage doors to look like wood really makes a huge difference in the overall 'curb' appeal of your home.