Upon entering the haram of Makkah, (the boundary lines of Makkah defined by Prophet Ibrahim) it is sunnnah to say:

O Allah, this is the place to which You granted a special status and made a place of safety. 

اللهم هذا حرمك وأمنك

So protect me from Hellfire. 

فحرمنى على النار

Give me safety from Your torture on the Day You resurrect Your slaves. 

وآمنّي عذابك يوم تبعث عبادك

Make me one of Your waliyys and one of the people who are obedient to You. 

واجعلني من أوليائك وأهل طاعتك

Upon reaching Makkah, it is sunnah to perform a purificatory bath (ghusl).
One needs to protect oneself from harming the people in the crowds in Makkah, because it is sinful to do so intentionally. Rather, one needs to act kindly towards others who might be crowding one.

When one first sees the Ka^bah, one raises one’s hands in du^a’ and says:

O Allah, increase the honor, greatness, nobility, and veneration of this place (the Ka^bah).

اللهم زد هذا البيت تشريفاً وتعظيماً وتكريماً ومهابة

O Allah, grant to the one making Hajj or ^Umrah, who glorifies and honors this place, more glory and generosity and higher status and endowments.

وزد من شرفه وعظمه ممن حجه أو اعتمره تشريفاً وتكريماً وتعظيماً وبراً

O Allah, You are the One Who is clear of all defects. And You are the One Who grants safety.  Usually, people have a great respect for the area of the haram of Makkah and avoid killing and committing injustice there. Even in the Era of Ignorance, they never fought there. Even if the person found the killer of his father inside the haram of Makkah, he would not kill him there. To do an injustice inside the haram of Makkah is more sinful than doing the same injustice outside of it.

اللهم أنت السلام ومنك السلام

O Allah, grant us safety from illnesses and defects.

فحينا ربنا بالإسلام

One makes any other du^a’ which one likes, asking Allah for things one is interested in from the good issues of this world and the Hereafter. It was reported that the du^a’ the Muslim makes upon first seeing the Ka^bah is answered. Then, one enters the mosque with the right foot and says:
I start with the Name of Allah, Praise be to Him.

بسم الله والحمد لله

O Allah, raise the rank of Prophet Muhammad and his Al and protect his nation from that which he fears for them.

اللهم صلّ على محمد وعلى آله وسلّم

O Allah, forgive my sins.

اللهم اغفر لى ذنوبى

Open for me the Gates of Your Mercy (Guide me to the ways in which I may earn Your Mercy).

وافتح لى أبواب رحمتك