When to use you: Use you or your when your product is asking questions, giving instructions, or describing things to the user. Just imagine what a personal assistant might say.
When to use me: Use I, me, my, or mine when the user is interacting with the product, like clicking a button or selecting a checkbox. But only add these words if you absolutely need to for clarity.
This little change got me thinking about a bigger question: Why do products sometimes label things as my stuff, and sometimes label things as your stuff?