If you're doing a single longform story for the first time, consider an episodic or semi-episodic structure. Particularly for those used to writing on this sub, it's going to be much easier to get through a single story chunk each day if that chunk is its own contained narrative, rather than writing 500 words about two people talking in an elevator while they wait for the next plot beat to happen.

It's a marathon, not a race. Don't feel pressured to write a lot every single day if it's burning you out, but make sure to write something so you don't end up with an insurmountable sprint at the end. The reverse is also true: even if you're a planner at heart, don't feel pressured to stop when you're still fired up with something just because you've hit your daily writing goal.

Remember that at the core of NaNoWriMo, you're basically speedrunning a first draft. Nobody's expecting a masterpiece to come out on your first try at a story, and it's okay if there's parts that feel really barebones when you're jotting them down. You're going to end up killing your flow if you stop to try to dot every i and cross every t as you go, so just make it "good enough" and let it rest until you've gotten the whole thing done.

A somewhat unusual piece of advice for those like me who have trouble with that last piece of advice and with keeping up their flow in general: Create a separate file for "editing notes", and just jot down which chapters you know are gonna need revision as you go. My first one was just a simple list of numbers with different highlights to show how bad I thought I did, which is a lot faster than actually correcting the weirdness and mistakes and lets you move on without the mental encumbrance of remembering what you need to do later.