Everyone pick an impossible task, and then do it.

We have competing feelings in our minds, and sometimes those feelings are stronger than our "rational sides". Facing our fears might be a good exercise. Facing legitimate fears (fears where the danger is real) might be useful too, but I'm specifically thinking about irrational fears.

Fear of "monsters" a la Bloody Mary in the mirror would be a good one. (Do it).

Fear of bad luck or divine retribution. (Break a mirror, step on a crack, say the forbidden thing).

Fear of the dark in your own house. (Walk around in the dark, make it fun).

Fear of social situations. (Purposefully put yourself in situations you are uncomfortable in but that won't hurt you).

Fear of heights (Safely).

Fear of failure. (Fail at something and make no excuses).

The goal of this exercise would be to acclimate yourself to these strong emotions so that they don't override your other instincts/thinking when it is important. Part of the challenge might be identifying fears you are unaware of.

Serious rationality training would involve:

• Studying the relevant concepts that describe the process of reasoning, such as "argument", "reason", "definition" or "concept". This allows to talk about thinking, and to study what counts for rational or erroneous thinking (reasoning, arguments).
• Studying the tools for making thinking more rational, recognizing or avoiding errors in thinking, evaluating correctness of thinking. For example, taboo a word (make sure you have an understanding behind it), focus on a question (while completely stopping from making arguments about the previously discussed question in the context of which the new question appeared), explain which specific reasons (assumptions) about the discussed concepts your argument used.
• Having someone to point out errors in your own thinking. This is like learning language, or good manners: you make errors, they are pointed out, you learn not to make them in the future. As a bonus, the rules are not arbitrary, and serve actual goals, with understanding of this connection being part of the art. For example, you argue for a correct conclusion using a correct argument which in itself is not sufficient to come to that conclusion - this could be a very subtle error that needs pointing out.

The first two items of this process are reasonably accomplished by the Sequences, but of course the growth of cultural knowledge would be better facilitated by people creating actual curricula or ideally writing up their own lecture notes.

The last item, practice, requires a trained rationalist and a topic to discuss, any topic where we have sufficient wealth of concepts to trip over and insufficient understanding to have answers that are not already cached to correct values and need actual reconstruction.

Choose topics including some where you have a lot of experience, and some where you have little or none. Write about what you believe in those areas, and how much evidence you actually have for those beliefs.

Some ideas:

• try to develop social practices for helping each other be good rationalists, to identify each other's successes and flaws at being good rationalists, to improve the dojo, to admit your own mistakes, uncertainties, and limitations, and so on.
• pick a relevant topic and have a conversation about it. The topic could be:
• a public issue where there's disagreement
• a personal problem that one of you has where applying rationality could be helpful
• a subject matter (like dating, eating, investing, charity, or working productively) where lots of people could benefit from applying rationality
• a relevant article that you all have read - either a LW post, or a published psychology article, or HPMOR, or one of the many things linked from LW

A different person could be in charge of each meeting - they might pick out an article and tell everyone to read it before that meeting.

One question is whether you want to focus your attention broadly on lots of skills & topics or narrowly on mastering a small number of skills or topics.

You could also approach one topic from many angles. For instance, with happiness you could first read some articles on the psychology of happiness (or a book like Jon Haidt's). Then have a meeting where you talk about happiness in your own lives: what makes you happy or unhappy, things you try to do to be happier, ways you might be irrational about pursuing your own happiness, changes you could make. Then each come up with a plan for improving your own happiness, and discuss & refine those plans so you're ready to carry them out. Then each try out those plans, and occasionally check in on how they're going and do group problem solving if they run into snags or you're ready to move on to a further plan.

Program something.

Although I have no idea whether programming actually is suitable cross-training for rationality, surely practice at analyzing a problem and breaking it down to bite-sized abstractions and interfaces will help form good habits. Those habits should become a standard tool in your mental toolbox.

Similar to jasonmcdowell's idea, practice doing instrumentally rational things in the face of conflicting (preferably non-irrational) emotions.

Any updates?

Look at the recently posted reading list. Pick some stuff, study and discuss. If you have a good "fighting spirit" and desire to become stronger, don't waste it on writing fanfiction...