First, determine the directions: up, down, left, right. Draw a horizontal straight line to be your horizon line. It separates everything above the viewer’s eye level with everything below. The cube will get smaller in the distance toward a point on the left and a point on the right. These are your vanishing points.
Now determine where the front-facing edge of the cube will go. Draw a line from each vanishing point so that they meet at a 90 degree angle at some point. If this meeting point is over to the right you will see the cube turned right and if it is more to the left you will see the cube turned left. Draw a vertical line from this meeting point. Somewhere on this line will be side G of your cube (see the example cube below).
Measure the distance from each perspective point to this distance point. Measure these same distances across the horizon lines. This lines determine your measuring points. The measuring points will figure out how far back you will need to go to get from the front face of the cube to the back face. That’s later.
Pick a point along the vertical line. This will be the bottom front corner of the cube, corner 4. The higher up you go the higher the cube will appear. If it is below the horizon line you will be seeing the cube from above. If it is above the horizon line you will see the cube from below.
Draw lines from this corner to the vanishing point. Along these lines will be sides C and F. If you want your cube to be in the correct field of view, the angle between these lines should be greater than 120 degrees. Anything less than this distorts the cube and it won’t look right.
From corner 4 draw a line up however tall you want the cube to be. The exact height of the cube depends on the viewer’s distance from the cube. This is the final side G. Then draw horizontal lines of the same length on either side from corner 4.
From the ends of each of these lines you just drew, draw a line to the opposite measuring point. Where these lines intersect the vanishing line to corner 4, there will be corner 2 and corner 6. Connect these to corner 4 to draw side C and side F.
Draw lines from the top corner back to each vanishing point. Then draw vertical lines up from corner 2 and corner 6. Where these lines intersect will be corner 1 and corner 5. Connect these corners to draw sides A, B, D, and E. You are almost there!
Finally, draw lines from corner 1 and corner 5 back to the vanishing points. Where these lines intersect will be corner 3. Connect these corners to draw side H and side I.
You are finished!
