This is the approved revision of this page, as well as being the most recent.
When should this bracha be said?
Upon seeing the sun in its original place in its orbit one should recite the bracha of Oseh Maaseh Beresheet. This bracha is made once every 28 years on a Wednesday in the beginning of the season of Nissan in the morning. 
Ideally, this bracha should be made immediately at HaNetz in order to fulfill the concept of Zerizin Makdimin LeMitzvot (the righteous are eager to do mitzvot early). However, if one didn't say it early in the morning, one can still say the bracha anytime before Chatzot (midday). 
It is the custom in Jerusalem to pray Shacharit at sunrise on the day that we say Birkat Hachamma and go outside the synagogue after Kaddish Titkabal and say the Beracha joyously with chapters of tehilim related to the event. 
There are multiple minhagim regarding how Birkat Hachamma is recited and every practice has a basis. 1: Some congregations have the hazzan recite the beracha out loud while everyone else recites it quietly. 2: Some congregations fulfill their obligation by answering "amen" to the hazzan's beracha. 3: Some congregations listen to the hazzan's beracha and say it aloud after him, just like the practice for the counting of the omer. 
It's better to make this bracha should together with a congregation.
Text of the bracha and prayers
Before the bracha, one should say "Haleluya Halelu Et Hashem" and after the bracha one should say "El Adon" until "VeChayot HaKodesh" and then Alienu and Kaddish. 
↑Shulchan Aruch 229:2 writes that upon seeing the sun in its original place in its orbit one should make the bracha of Oseh Maaseh Beresheet. Kitzur Shulchan Aruch 60:6, Mishna Brurah 229:8, and Yalkut Yosef, Hilchot Berachot, Siman 229, laws of Birkat Hachamma, Halacha 2 agree.