I'm not sure what a normal way to say this is, like if someone comes into your office. Would it be veuille t'asseoir ? What other ways are there ?
I mean it in the sense of offering someone a seat. If there is any connotation of requesting they sit, that's important to know.
Like in English, please sit could be taken slightly different ways depending on your tone and relationship with the other person, whereas please be seated is very unambiguous and generally used in professional contexts like a flight attendant speaking to passengers.
Edit: Apparently veuille t'asseoir is not said; veuille is never used. I am not surprised, as I have never once heard it used before, but I was sort of testing the waters. So I have to say veuillez vous asseoir even in situations that call for tu ?