How much of a plan do you carry into games? After you see the match up or figure out the deck you are against, how much of your game is in-the-moment reactions to the things in front of you and how much is dictated by specific or general plans of action worked out in advance?
It is definitely a bit of both. My deck will have a game plan which I will try to follow. But I might have to stop my opponent from achieving their game plan first.
A typical example is coming up against Whizzard. Whatever your corp deck is trying to do (kill, glacier, etc), it first needs to stop Siphons as this will most likely stop you achieving your plan. If your plan is to win the econ race, you probably then want to stop Temujin so putting ICE on all three centrals is not a bad first turn. If you are playing a trap deck you might not care if they get their temujin money.
I think that aspects of deck construction, be it taking a specific archetype or choosing to include certain silver bullet cards, is where the conversation starts. That being said I think generally the statement “failing to plan is planning to fail” fits netrunner, you should have a specific gameplan and the spur of the moment stuff should be a rare deviation of that gameplan in response to what the other person does. Again some corp and runner decks are more effective at having their own plan (eater keyhole siphon, moon HB, most successful and popular decks really), whilst other decks are more reactive, where a plan might be more specific to each matchup, rather than focusing on getting all your key cards on the table and forcing out agendas/disrupting the corp’s plan regardless of what it is via whatever runner tools.