I have some strong suggestions.
You no more than fives rules, and they should be simply stated. For example, these serve me well:
- Be Respectful.
- No Hate Speech or Bullying.
- Keep your content Relevant.
- Links, Images, Memes, and Videos.
- Don’t waste time.
Five rules because that’s about the most anyone can remember, even the moderators, so keep it simple.
Explanations and interpretations of the rules can be much longer, paragraphs longer, and this text should be linked or readily available where people can find it.
#1 Respect covers a multitude of sins aside from just being nice to other people. Spam is disrespectful, p0rn more so, etc..
#2 is really part of #1, but sometimes you really want to emphasize a certain point.
#3 Content should be obviously relevant. A question, an opinion, a topic for discussion, or a written description of linked content and why they think it is worthwhile. Auto-generated text or text within an image doesn’t count - the OP was to actually write something about it. Moderators should judge relevance by how the OP introduces the content, NOT by judging the content itself. If it isn’t obviously relevant, then moderators are free to approve/remove the content as they see fit. It is the OP’s responsibility to make their content relevant when they create the post.
This rule makes a moderator’s job much easier, because it reduces difficult judgement calls. It’s also very easy to meet this bar for relevance, only minimal effort is required (but Spammers won’t make this effort).
#4 Link to a longer statement of policy about media content, minimally “No Naked Links”. A picture might be worth a thousand words, but most memes are not.
#5 A catch-all for other situations and content. Hard decisions demand too much of your time, so bounce any content that isn’t an easy decision. If some content or comment is not obviously appropriate, then it’s NOT appropriate. In other words, if you can’t quickly decide if something is appropriate or not, it’s not the moderators job to fix it. Send it back to the OP and ask for changes. It’s also useful for rules-lawyers or anyone who’s sole purpose in life is to make more work for the moderators.
I also have a Rule #6, which states, “There is no Rule #6, but now we know you read this far.” I ask “What is Rule #6” in the New Member questions on FB, and the answers are quite revealing. 
I see some FB groups with 10-15 rules and have to laugh. There’s no way to have that many rules and not have them be redundant, or worse, contradictory. Either the author hasn’t really thought it, or they are a control freak, or both.
Consistency is absolutely necessary. Moderators need to communicate with other mods so they know how situations are being handled. Mods should also avoid moderation discussions/arguments they are a part of, so to avoid the appearance of bias. Call in another mods to handle the situation as needed.
Like it says in Discourses’ FaQ:
The point is that Images/Memes/Links/Videos should be presented with some additional text the mods can use (and other readers). If the OP makes a good effort then mods should approve it. If not the mods can remove it with minimal time wasted. It’s the effort that counts, and Spammers won’t make any extra effort.
