I have been a furry for 10 years now I started doing art when I was 17. At the time we all followed a list of rules. We drew pics based on these rules. While the rules are not the law you do not have to worry about the cops locking you up for breaking a rule. These rules are just classic critique to help you draw art that not only appeals to the majority of our fandom but also give us a decent reputation.
(Note some is just for humor/sarcasm)
The rules were listed by
1.) Furry characters shall not have a human facial structure (jaw, chin, eye socket, etc). They shall have the base animal's facial structure, though it may be stylized. Human hair on the head is OK.
2.) Furries shall not have human lips.
3.) Furries shall have animal paws with pads, not human feet with long toenails.
4.) A comic that involves noble furries fighting for freedom against evil hyoomans shall be an object of scorn.