I'll be brief, so that everybody will read it (hopefully
):
1. Read the rules thoroughly and understand them
2. Investigators, make investigations every day; set up a proxy chain of length 1 or 2 (i.e. tell one other person that you are investigator, and have them announce results for you.)
3. If you have protection (ironheart/medkit) or an activated mic/receiver pair, try to get killed. Consider it a big victory if you die to take down a mafia.
4. Let someone else know if you are going to be alone with someone or are likely to encounter someone.
5. Communicate suspicions on the forum, or at least to a few other people by private message.
6.
DON'T last minute Lynch Mob. This is a great way to accidentally kill an important role or someone who's innocence can easily be verified. Last minute lynch mobs are the mafia's best friend.