one-point perspective Cube
Start by drawing a horizon line (with a ruler), and one vanishing point.
The horizon line helps as a guideline to draw other parallel width lines, AND to see how close objects are to the horizon line, and therefore how foreshortened they are.
The vanishing point is the meeting point for depth lines. The closer objects are to the vanishing point, the more they are foreshortened.
Next, draw a rectangle.
Remember:
In one-point perspective, width lines are parallel to the horizon, and height lines are perpendicular to the horizon.
Now draw depth lines from the rectangle's vertices (corners).
Depth lines meet at the vanishing point:
Determine the amount of foreshortening (the depth's length), and finish drawing a box in perspective:
Try draw some boxes above, on, and below the horizon line.