NOTE: For whatever weird reason, the video on Youtube has a weird glitch around 1:25, you can view the complete video without glitch on my facebook here.
There are many ways to go about drawing backgrounds and perspective. In my old Cityscape Speedpaint tutorial, I drew out some rough perspective lines by hand, similar to how one would do it with a ruler on paper. But with drawing programs, there are lots of shortcuts to use.
The technique I showed in this tutorial is good if you need lots of precise perspective lines quickly. Using free transform allows you to create endless combination of perspective lines from the few grid brushes.
I use Free Transform to give perspective to the paint cans in the same way I did to the building's windows in the cityscape tutorial. It's quick and easy, instead of having to draw out each can individually. You can use this technique for more than just paint cans of course. Try it out with other things like a room with a table and a circle of chairs around the table.
This is one of intermediate shortcuts I use, but in the future I will be showing you how to build actual 3D backgrounds for multiple use in comics :) and how to integrate the 3D generated backgrounds into 2D drawings.