I metagame the shit out of any more or less mechanically complex game before I start playing it.
I will read tons of guides and hints and will dissect the optimal powergaming mechanics (or at least identify noob traps and trash ones) before getting on with the game.
I will make mini-guides for myself for such games as well.
My first playthrough is always a (near-)completist one.
Out of curiosity, does this not spoil the game for you?
Not nearly as much as I had feared in the past.
Firstly, when powergaming mechanics, the plot twists are of a minor concern because I'm mostly focused on finding out how stuff works in the game etc.
In case some story events do influence how you game the game, I'd rather know about them in advance, and it actually brings me a good deal of satisfaction knowing that I'm prepared for the devs' tampering in advance.
Even then, considering the average "quality" of writing in the gaming industry, you can see the "plot twists" coming from the very moment you start learning about the game's plot. So, it's usually not the matter of that the "big reveal" is, but rather the matter of when it happens.
Additionally, most guides and discussions are usually sensible when it comes to spoiling the plot details, so they usually refer to those in a vague way that minimises the plot exposure anyway.
And finally, I found out that spoiling the plot in advance does not detract from the experience in the least! Not just in the games, but in the films and books as well. Because the spoilerific moments are just that - moments in the overall story, where a lot of other things happen.