Let's step it up a level with more complex shapes like a star or a circle...

COMPLEX SHAPES - STEP BY STEP

How does it work for more complex shapes like a star for example?

1. You start by drawing your flat shape. This will be your front side.
2. Determine the angle and how deep the extrusion should be and draw the edges accordingly from every corner of the shape, keeping them all parallel. 
3. Redraw the same shape displaced which will be the backside of this star shaped 3D object.
4. Erase all the lines that are behind the object and hidden from the viewpoint. This is a little more tricky because some parts won’t be as visible. But that’s where you train your spatial awareness muscle.

You don’t always have to draw all the edges from each corner. Any extrusion edge that hides behind the shape isn’t necessary. But I highly recommend, starting with it as you get the hang of it. It’s like having training wheels on a bike. It’s helpful and you don’t want to rush it. 

But it would be a bit like this:

Another complex shape (well, actually it’s more of a simple shape, but simple in design is usually more complex) is the cylinder. The difficulty in any curve is to find the outermost edge. The only two edges you’ll find are on side. 

In a perfectly round circle, the outermost point is always found by tracing a perpendicular line to the shadow direction through the center of the circle like this:

But here’s how you can also help yourself to draw the backside which is a transposed circle.

Draw more edges. Or as I like to call them: Helplines.

As with all the extrusion edges, keep them the same length and same angle:

You realize that tracing just got a lot easier this way as you have coordinates that help.

You can do this anytime when you have curves or complicated round shapes.