1. Nothing too sexual. The implication of sex and discussion of sexual topics is fine, but don't get too detailed or graphic outside of PMs. Remember that this isn't posted in the Adults Only section.
2. Read the lore before creating your character and starting to RP.
3. Only use original characters that make sense being on this planet (and are included in the species list).
4. Don't have your character do things that don't make sense - emerging from a difficult fight unscathed, miraculously finding a helpful item at just the right moment, etc. Make your actions believable within the setting.
5. Don't have a character start out with a huge advantage, like wealth, magic, etc. (magic is much rarer and more difficult to perform in this world than in most other fantasy worlds, so starting out as a competent wizard doesn't make sense.)