I don't know, but I'll throw some ideas up. These aren't all the possibilities and probably don't include the best possibility.

Each step must be moral taken in isolation. No it'll-be-worth-it-in-ten-years reasoning, since that can go especially horribly wrong.

Work honestly within the existing systems. This allows existing safeguards to apply. On the other hand, it assumes it's possible to get anything done within existing systems by being honest.

Establish some mechanism to keep moral intuition. Secret-ballot mandatory does-this-feel-right votes.

Divide into several conspiracies, which are forbidden to have discuss issues with eachother, preventing groupthink.

Have an oversight conspiracy, with the power to shut us down if they believe we've gone evil.