Well, I've actually pre-ordered the game, so I'll play it the second it comes out (ignore download times...)
And as to what I'd do, well - I suppose it'd be the same as what I did with The Witcher 3; start the journey by getting to know their characters, and try to figure out their back story (as I feel like the gameplay becomes a little more interactive and realistic if you know what you're trying to achieve, what you're fighting for; that is, instead of mindlessly going on a glorious rampage throughout the city, without really knowing what you're fighting for, and why)
I would obviously also customize my character to my liking, cranking up that "juicer (and juicers)" slider, as I will obviously be playing a female character, so I have something to look at and customize... also known as, their hair style, clothing style and other really important things. (Other than that, females in games usually have smaller hitboxes - maximum sweat and salt, zero remorse. ((don't @ me on this, it was a joke, I hope you weren't offended.)))
Also, considering the recent rumors where we get to interact in sexual events with the main characters as we go through an exciting bloodshed across Night City, I'd do what anyone else would've done, given my circumstances... make love with Keanu Reeves himself. As he's a main character, and if we were to have optional sexual intercourses between characters, he would be the obvious choice to have as a partner.
I was going to continue to write a longer explanation, but I have work to do, sadly. I would've loved to continue my epic story about mayhem, sexual intercourses, the game environemnt in general, gunplay and so on and so forth; but we all have stuff to do, other than write essays on a giveaway thread, haha.