I think an important part would be separating the "decision phase" from the "action phase".

In the decision phase, it is OK to speak whether it is a good idea or not, and even if it seems like a good idea, whether you expect yourself to do it or not. If almost everyone agrees that it is a good idea, and if enough people declare they would do it, the community consensus is published and we move to the action phase.

In the action phase, the decision is already made. People are encouraged to report "yes, I did it" and receive some special "action karma". Action karma would be a system for immaterial rewards to LW members. It is only possible to achieve action karma by doing things that have reached community consensus. Action karma is remembered forever.

The essence of my proposal is that we should have some "action karma", and the only way to reach it would be to do clearly defined goals. The goals must be declared as important, desirable and realistic by rationalist community by some mechanism that makes a yes-or-no decision.