One of the first skills you will want to practice if you want to make realistic-looking sketches is perspective drawing. Making accurate 3D illusions on a 2D surface was first done by Filippo Brunelleschi in the early 1400s. His technique, which we will practice here, was an important step in adding depth to Renaissance paintings.
One-Point Perspective 
Draw a line that represents eye level and choose a vanishing point. You don't have to put it at the center of the paper, but it's easier if you are just getting started. Leonardo da Vinci's Last Supper has the eye level and vanishing point where Jesus is.
Now draw a square or rectangle.
Lightly draw the lines of perspective from the four corners of your square or rectangle to the vanishing point then decide how far into the distance your now 3D shape will go. Remember to keep the lines parallel to the original square or rectangle shape.
Add a one-inch border and a bunch of shapes. Try adding Tetris-like shapes such as L or T shapes. You can show the hidden edges by drawing dashed lines.
Remember to sketch lightly because you will want to erase all of the lines of perspective and the eye-level line later.
When you're done you should have something that looks something or hopefully better than this.
Two-Point Perspective
This time you will have two vanishing points on the eye-level line which should be out of the border at the very edges of your paper.
Draw a random verticle line then extend the edges to the two vanishing points. Drawing in two-point perspective is actually easier than in one-point perspective because you only need to draw one line then let the edges extend to the vanishing points.
You will know your 3D shape is accurate if your hidden edges all lineup. The back hidden verticle edge should be parallel to the original line you originally drew in the front.
Add a bunch of shapes. You can add the hidden edges or dashed lines to some of the shapes or erase them in the end. Try to have different shapes and some overlapping to add depth.
And that is how you draw rectangular shapes in one-point and two-point perspectives. Thank you for reading. Have a nice day. Now get drawing!
Resources:
https://en.wikipedia.org/wiki/Filippo_Brunelleschi
https://en.wikipedia.org/wiki/Last_Supper