I'm having great trouble keeping my present and past tenses straight in the second person. Why is that? Are there any different rules that my brain is defaulting to that I just don't consciously know?
Second-person present tense is good for the immediacy of a choose-your-own adventure story. It's a less familiar way of telling a story for most of us than than first-person + third-person past tense. In second-person present tense, I find it easy to veer back to past tense, and then I go back and catch and fix it. Why? Familiarity, probably. What the folks who study slips call "capture error", it's easy to fall into the more common phrasing.
Now that you mention it... That is a surprisingly easy mistake to make. I had to rewrite several parts of a few posts I recently made just because of that mistake.
Strangely, that's a problem I never had, but maybe that's because I am used to writing reports and features, where the idea of "being right at the spot" is key. I guess that's also what might help while writing stories: Imagine yourself (or the protagonist) right there, at the spot. That's, after all, how the reader should feel: He is right there, in that moment, and now has to decide what do to. Everything that happens, happens in real time. It's not a story, that's been told afterwards, it's a description of a situation which is happening NOW.
I move between stories where it goes form you to I and it kills me inside, even though I check I am 100% positive it is something I fucked up