How do I create a good portfolio?

You are about to attempt to get a graphic design job, so you will most likely need a portfolio. So, how would you structure yours? What should you put into it, and what should you leave out?

In case you are developping a digital portfolio, and if you choose to have white background, if possible turn down the brightness by adding 10% black to the white. This emans, don't make it plain white and go with a subtle shade of grey. Keep the layout design nice, clean and even minimal for the same reason as you don't want people to be distracted by bright and vivid colors aside.

There are a lot of ways that you can choose in creating a good portfolio. You can even search it online.
Anyways, just wishing you all the luck.