ImageOptim (OS X) is a great GUI tool for optimizing images if you don't know/feel like setting up a gulp/grunt task.

You should also be aware that you can optimize SVGs as well with SVGO (also has gulp and grunt flavors).

I also wish the article went into new upcoming image formats like WebP, BPG, and FLIF. But those are probably a long way out if they ever get widespread support.