Less Wrong members sometimes arrange meetups (or “dojos”) to meet each other in meatspace. Some geographic areas have groups that do this regularly. This page lists tips and resources for Less Wrong meetup groups.
There is also a facebook group for organisers to talk to each other
Most of this data comes from the post Less Wrong NYC: Case Study of a Successful Rationalist Chapter. (For more on Less Wrong NYC, see Epistle to the New York Less Wrongians.)
Communities need heroes. Most people will be passively attending. Step up.
Commitment works. Announce regular dates and times, and stay for a minimum length of time, regardless of attendance.
Schedule events first, get feedback later. Getting everyone to state their preferences up front leads to prolonged indecision.
Be a group of friends. Meet regularly. Do things you like doing, together. Be a community. Set goals and hold each other accountable. Be honest. Make use of each person’s skills and knowledge.
Gender ratio matters. Treat others with respect. Be mindful of exclusionary language.
Use the mailing list for more than just meetup scheduling.
Interact with outside rationalists as much as possible.
Congregate in the area nearby with the most Less Wrongers.
Social / unfocused discussions. Attendance is usually poor; members report that hanging out is harder to justify than having a specific purpose.
Specific discussion topics. Attendance is good. Break into small groups to make better progress.
Presentation / skill training. Attendance is good if the topic interests many people.
Group planning / meta. Usually just for group leaders.
Structured exercises. Attendance varies. Example from NYC Less Wrong: Fun and Games with Cognitive Biases.
Tell your rationalist success story.
Basics of rationality.
Feel free to contact lesswrong user Elo to ask questions about planning or running a meetup.