Travel in pairs (sometimes): While sometimes risky, having a witness can be invaluable. If you're with someone and they kill, you know who the Impostor is. If someone kills you, at least your partner might report it.
Watch those "visual tasks": Some tasks have unique animations (like MedBay scan or diverting power in Electrical). Seeing someone perform one confirms they're innocent.
Don't be afraid to accuse: If you have strong evidence, present it calmly and logically. But also be prepared to defend yourself if you're wrong.
Prioritize critical sabotages: If the O2 or Reactor is sabotaged, fix it immediately! Winning by tasks becomes irrelevant if the ship blows up.