Mezuzah

When putting up a Mezuzah (or Mezuzos), place the Mezuzah in position on the wall, and partially knock the nails in. Then say the Brocho:

ברוך אתה ד' אלוקינו מלך העולם, אשר קדשנו במצותיו, וצונו לקבוע מזוזה

Immediately after the Brocho, complete knocking in the nails.

The following are some halachos regarding the Brocho on Mezuzah. (the list is far from complete)

• Make sure the doorpost requires a Mezuzah
• The Brocho should be said while standing
• There should be no waiting in between the Brocho and the completion of the placement. If one accidentally waited but kept his/her mind on the Mitzvah, he/she does not have to repeat the Brocho provided he/she did not speak. If one spoke after the Brocho (but before the affixing), he/she must repeat it unless the speech was for the purpose of attaching the Mezuzah.

For more Halachos, see the Sefer referenced below, find a different sefer on Hilchos Mezuzah, or ask your local Orthodox Rabbi.

Source: The Complete Mezuzah Guide