Make sure that your painting surface has the same height-to-width ratio as the reference photo. Refer to the online ratio calculator in the Resource Section below.
Draw guidelines on your spare reference photo. Lay the ruler's edge against the straight lines in the photo and draw reference lines that extend beyond the wall and into the distance. The most important lines are the tops of the walls, or where they meet the ceiling, and the bottoms of the walls, or where they meet the floor or ground. If a row of same-size doors or windows runs the length of a wall, the tops or bottoms will create more lines that you can trace.
Find the vanishing point. The lines may not actually meet at the exact same point, especially if there is some distortion in the photo, but there is a general area in the distant part of the image where all of the lines will converge. This is the vanishing point.
Use the pen and ruler to highlight other important lines such as the vertical lines that indicate where the walls begin and end.
Draw the reference lines on your painting surface. Use a graphing technique or draw freehand. For watercolor, use light pencil lines that can be erased or obscured by paint. With oil or acrylic paint you can be less careful because the lines will be hidden by subsequent layers of paint. Pay special attention to the placement of the vanishing point and to where the lines run off the outer edge of the paper. If the walls are in front of you (as in the second photo), then the lines will not run off the paper at all. In this case you will draw vertical lines to indicate the closest edges of the walls.
Fill in the details. Use the reference lines to guide you as you create your painting. Place other objects and textures in relation to your guidelines and you will create a convincing illusion depth, and of parallel walls that recede into the distance.