Alright, here we'll try to make a basic cube and that's pretty much how you do everything.
We start with the horizon. Every somehow realistic drawing usually has one, since it also determines whether it's bird's view on the picture or whatever.

Then we mark the vanishing point. It can be anywhere on the horizon or even off the horizon. There can be more of them. It's a pretty important "tool" when it comes to perspective.

Now, to draw a cube from any view, we have to start with a square.

You connect the angles with the vanishing point. Now you see where this is going, huh?

Whenever you try to make a correct shape in the 3D view, it's really important to remember the lines should be parallel.

Now connect everything like this.

Erase all uneccessary lines and there you go.
Now everything pretty much follows this principle. How does one draw a pyramid?
First you draw a cube the same way we did above and connect the inside corners of the upper part of the cube to get the middle.

And now connect the lower angles.

This may look pretty simple, but you can create pretty realistic drawings of buildings using this technique.
Check out this:

His horizon was probably the green line I've marked and two vanishing point. I'm pretty much guessing here, but I know I'm close.

Or here for instance the vanishing point is in the middle.

Puinkey, I hope this helps. All images kindly provided by Paperclip.