Science/rationality subjects to teach

Take on subjects that are frequently tackled, like career advancement and well-being, but with actual scientific backing to what you say.

Specifically, I think "How to negotiate" is a great subject; You can cover both the basics of how to not negotiate against yourself in business, and also how to negotiate with your SO, how to seek win-win solutions and frame them to others, and many other things.

Nutrition and exercise interest a lot of people, and a classroom is a good place to give them the simple facts without advocating fad diets or anything (people seeking information on the internet have to wade through a lot of uninformed zealotry in these fields).

Economics and personal finance are great topics too. You can cover everything from the psychology of budgeting to risk management in investment to tax optimization.

Remembering that teaching people about biases can be harmful, I would probably stay with something like: "keep thinking for five minutes", "leave yourself a line of retreat", and maybe something about politics being a mindkiller (to make people less guilty if their solution to a problem includes something that doesn't belong to their party's slogans: cooperation, charity, competition, market,...).

But as an instrumentally useful thing, I would teach people using Anki and wikidpad, and a simplified version of GTD. There would be some theory about how computer is your extended memory and good note-making leaves you more free working memory for thinking; and how human memory and spaced repetition works (for things that cannot be handled by making notes, such as learning a foreign language). As a practical exercise I would give students some information printed on paper that they would have to put into the software. A list of foreign words and grammar for Anki, some know-how and contacts for wikidpad, and some projects and ideas for wikidpad in GTD style. At the end, I would make them think about their own plans, and prepare GTD projects for those.

Basics of habit formation research, basic mindfulness techniques. Should definitely include exercises.

Summary of happiness research (see e.g. Lukeprog's posts).

Existential risks to humanity, and what sort of things avoid those risks (e.g. talk about catastrophic asteroid impact likelihood, effects, and the feasibility of colonizing other bodies in the solar system, or mitigating bad stuff some other way).

What's your existing skill set?

Real life applications of game theory, along the lines of Schelling's book.