There are a bunch of things I do when I re-install macOS on a computer, or when I begin working on a new computer. I don't do this often, so it's easy to forget the steps. So I documented everything in a gist.
I used to keep these steps in Notes.app but figured they should be public anyway (open source by default, right?) so here we are.
One thing I've added recently, that's super-important to me, is to untrust a certain certificate. Blue Coat is a company that creates internet surveillance and censorship software and Semantic gave them an intermediate CA certificate. That means they can sign arbitrary certificates that you're computer will trust (because your computer trusts Semantic, and Semantic trusts Blue Coat).
I'm not really into the idea of my computer trusting a company like Blue Coat, so I follow the instructions to untrust this certificate. I highly recommend you do, too.
And I recommend you document everything you do to make your computer awesome!