It is reported from Sayyiduna Abdullah bin Bishr that Rasulullah said: "Do not stand in front of doors of houses (you visit) but (rather) stand on either side of the door to seek permission for entry. If you are permitted then enter into the house otherwise return."
It shows we must not inconvenience anyone by blocking the doorway, and if you'r not allowed in then leave. That is basic Islamic etiquette:alhamd:.
:jz: for reminder. Islamic etiquettes are beautiful.
Also when knocking not to exceed 3 times.
Seeking permission to enter three times:
It is narrated on the authority of Abu Musa al-Ash'ari (may Allah be pleased with him) that the Messenger of Allah said: "Seeking permission is three times. If you are given permission then you can, otherwise return." [Agreed upon: 6245 - 5633]
Scholars have applied the above rule for mobile phones aswell. So don't exceed 3 times when calling someone.