I learned from Rabbi Zvi Drapkin Shlita (Rosh Yeshiva Grodna - a branch of
the Ponovez Yeshiva) that one cuts his Ethrog prior to Rosh Hashanah of
the 7 th year and after Rosh Hashanah of the 8 th year. (This is based on
the rule that Ethrogim go according to the year in which they were cut -
see Mishnah Bikurim.) One has to make sure that he takes Teruma and Maaser
here in Israel. It is forbidden to take fruit with Kedeushat Sheviit out
of the land of Israel. In the States, it is best after the Shemitah year
to buy Greek Ethrogim. It is a mitzvah to eat the holy Shemitah fruits
and not let them rot.
That is almost a book or two of Halachot in a nutshell.
Richard (Rachamim) Pauli