What are the common words for "clean" and "dirty", "tidy" and "untidy"? For example, how do Chinese speakers normally say:

Your room is so clean!
Your room is so dirty!
Your room is so tidy!
Your room is so untidy!

脏 Is this the most common way to say dirty?
I agree with @Tang Ho's answer but I'd like to add something here. 

Orally, people tend to skip the word "的" and may use "好" instead of "真". 

1. Your room is so clean! 你房间好干净啊。
2. Your room is so dirty! 你房间好脏啊。
3. Your room is so tidy! 你房间好整洁啊。
4. Your room is so untidy! 你房间好乱啊。


Note that I added a modal word "啊" at the end of each sentence. This is because there is a slight difference between "好" and "真".

"好" is a milder tone and the speaker is trying to address their feeling about the cleanness or tidiness of your room. If the speaker uses "真", the speaker emphasises more on the fact that the room is dirty.

And "脏" is the most common way to say dirty.