A more comprehensive list of rules than "Don't be a dick" for the main post would probably be a good idea, so if anyone doesn't mind me writing up a first draft for it then here goes.
1: Don't be directly offensive to another forum member in an aggressive or hateful manner.
2: No directed racism, or comments that follow the actual definition of racism, such as being said in a hateful manner.
3: Don't spam, double posting is fine occasionally as long as there is a reason to do so.
4: Offensive, sexual, seizure inducing and questionable content should be placed behind a spoiler with an appropriate warning clearly written in the post. (Perhaps have an official colour for content warnings?)
5: No links to webpages that you know aren't safe, or may be questionably safe.
6: Do not attempt to work around a ban, doing so will likely result in an even longer ban or permaban.
A specific list of rules for Mod behaviour seems like it would also be a good idea, although so far all I've got is
1: Do not cause "The Moddening"