Why does my brain freeze when I have to choose between passato prossimo and imperfetto?

I’m a false beginner; I can read news articles reasonably well, but as soon as I try to recount my day to an Italian friend, I completely blank on which past tense to use. It feels like a guessing game that makes me sound like a robot. Does anyone have a mental framework that actually helps keep these straight when you're mid-sentence?