There are many general rules that people created over time. Tea ceremony has very precise and strict rules to prepare tea both in matcha (powder green tea) tea ceremony and sencha (leaf style green tea) tea ceremony.  These complex array of rules are often intimidating to beginners and casual tea drinkers.  I didn't like the rules either, especially they do not explain why things were the way they were, but if you understand the reason behind it, it is not very mysterious any more. 

We will look at sencha here.