This is one of the greatest Sunnahs on the day of Eid because Allah says (interpretation of the meaning):
“(He wants that you) must complete the same number (of days), and that you must magnify Allah [i.e. to say Takbeer (Allahu Akbar: Allah is the Most Great)] for having guided you so that you may be grateful to Him” [al-Baqarah 2:185
The time for takbeer on Eid al-Fitr starts from the night before Eid until the imam enters to lead the Eid prayer.
Allahu akbar, Allahu akbar, laa ilaaha ill-Allah, wa Allahu akbar, Allah akbar, wa Lillaah il-hamd (Allah is Most Great, Allah is most Great, there is no god but Allah, Allah is Most great, Allah is most great, and to Allah be praise).
The etiquette of Eid also includes the congratulations and good wishes exchanged by people, no matter what the wording, such as saying to one another Taqabbala Allah minna wa minkum (May Allah accept (good deeds) from us and from you” or “Eid mubaarak” and other permissible expressions of congratulations http://dlvr.it/6RgLLn