Even though shadows are very complex, you can already draw them, you just didn't know it.

SHADOWS

Let's first remind ourselves what’s necessary for shadows:

Without a light source, there is no light. Duh! However it’s so easily overlooked.
So where does the light come from and which elements does it really touch?

And to see a shadow we also need a surface to cast the shadow on. 

So, the key factors are the following 2:

1. Position of the light source
2. Which side the object is lying on?

You always have 3 options. All 3 sides that aren’t visible could be touching a surface:

Example

This is the most common method used in lettering.

The object is attached with its backside to a fictional wall & the process for the cast shadow is exactly the same, except that you start with the backside of the cube.

1. Select the side that the object is placed on. (in this case the backside)
2. Choose at which angle the shadow is cast and how long it is.
3. Connect the visible corners and hide the lines that are behind the object
4. Color in the shadow part.

In most cases you want to counter the angle of the 3D extrusion, otherwise it just might look like and extension to the extrusion, even though there is nothing wrong with it.

Lastly to explain why the shadow is casted this way we need to visualize how the light travels. Because, what if there’s another object that had a different height? How much does the shadow need to increase…?

Contrary to popular belief the angle of the light isn’t the same angle as the angle of the cast shadow.

Let’s find out

The shadow only appears where the object blocks the light. So the outer most edge of the cube (the top right corner) is where the light will travel and hit the floor or surface. Everything between the cube and that the part where the light hits the floor is shaded. 

So, how about when the object is smaller or taller, how do I know how long the shadow should be?

The shadow triangle is really helpful to determine the length size of the shadow and just needs to be scaled up or down. 

And lastly, the shadow on the object itself.

The goal is to also differentiate all the sides from each other to create a stronger contrast. 

But finally, it will need to make sense to accord the applied drop shadow to the direction of the light.