Rule 1: All latte art must be created with the utmost care and precision, lest the milk foam resemble a toddler's plaything.
Rule 2: No latte art shall be created with the intention of making the barista's life harder. That is, unless you're trying to make a point about the futility of human existence.
Rule 3: The ratio of design to designee (the object being designed) must be at least 2:1. Otherwise, it's just a mess of milk and wobbly lines.
The Steampunk Latte Art Subpage has further guidelines on incorporating gears and clockwork mechanisms into your designs.
Visit the Latte Art Guild Certification Program for information on becoming a certified latte artist.
And don't even get us started on Latte Art Holidays. Those are just excuses for us to make more rules.
Remember, latte art is not just a trend, it's a lifestyle.