1] NO BEING MEAN. It's the number one rule for a reason. I leave my icons public so everyone has access to them not for people to come by and put ones they don't like down. Some people enjoy them, others don't. Some computes show them looking amazing, others make them look like crap. It varies so please be nice.
2] Comment when taking icons. Credit is nice but not necessary to use them.
3] If a specific post has rules please follow them.