To fulfill the mitzvah one takes one etrog, one lulav, three hadassim, and two aravot. The etrog is taken separately in one hand, while the lulav, hadassim, and aravot are bound together and taken in the other hand. (The word lulav is often used to refer collectively to this bundle.)

When binding the lulav, its spine is placed facing the person, and the hadassim and aravot are tied to its right and left. There are various customs as to how they are placed; the Chabad custom is to place one aravah to the right of the lulav and the second aravah to its left, and cover them with the three hadassim —one on the right, the second on the left, and the third atop the lulav's spine, leaning slightly to the right. (Others place the three hadassim on the lulav's right and the two aravot on its left.) The lulav, hadassim, and aravot are bound together with strips of the lulav leaves. The lulav itself is bound at two points (above the knots made to bind the hadassim and aravot) so that the leaves of the lulav do not come apart when it is waved.

The lulav bundle should be bound before the advent of the Festival. If one failed to do so, or if the knots came open, it may be bound on the Festival provided that one binds it with a knot that is not considered to be permanent, for it is forbidden to tie a permanent knot on the Festival.

Since two species are bound together with the lulav, the lulav is taken in the right hand while the blessing is recited. The etrog is then taken in the left hand. It should be held in the direction of its growth, with oketz (the bottom of the fruit, where it was connected to the tree) on the bottom. One then brings his two hands together and, facing east, shakes the lulav bundle and etrog in all four directions "toward the four sides of the heavens," as well as up and down, in this order: right, left, forward, up, down, back. One should be standing during the blessings and the "taking" of the lulav bundle.

(Others have the custom of holding the etrog upside down while reciting the blessings, and then turning it right side up before performing the mitzvah.)

It should be noted that if any of the species is held upside down, the mitzvah has not been fulfilled. According to the Torah, whenever performing a mitzvah with something that grows, one must use it in the direction that it grows. We derive this principle from the Mishkan (the Tabernacle in the wilderness).

Normally, when one constructs a house, the boards or planks are laid horizontally, one above the other. Regarding the boards used for construction of the Mishkan, however, it is written: And you shall make the walls of the Mishkan from acacia wood standing up (Exodus 26:15) - i.e., the wood used for the outer walls of the Mishkan was placed vertically (in the direction that it grew) rather than horizontally.

There are some authorities who are stringent and rule that there should be no foreign body intervening between the person's hand and the four species. They therefore rule that one should remove rings from one's fingers before "taking" the four species.

The mitzvah of "taking" the four species applies only by day and not by night.

Our Sages decreed that the mitzvah of the four species is not performed on Shabbat - even if the first day of the Festival (when taking the four species is a Torah obligation) falls on Shabbat. They did so because they feared that in taking the four species one might come to desecrate the Shabbat by violating the prohibition of carrying an article in a public domain. (This decree is similar in concept to the Rabbinic decree not to sound the shofar on Rosh Hashanah if it falls on Shabbat.)

Just as one cannot fulfill the mitzvah with species that have been stolen, one cannot fulfill the obligation with species that are borrowed.

One can only fulfill the obligation if the species are presented to him as a gift rather than as a loan, for the Torah prescribes that You shall take for yourselves on the first day; that is, the species used on the first day must be the property of the person "taking" them. This applies on the first day of the Festival and, outside the Land of Israel, on the second day as well. On the remaining days, one can fulfill the mitzvah with a borrowed set of species.

Therefore, on the first day of the Festival (and on the second day outside the Land of Israel) one should not give the four species to a minor to enable him to fulfill the mitzvah before one has done so himself. The minor can acquire ownership of an item but cannot transfer ownership to others. 

Thus, if one gave the four species to the minor, it would become his and he would be unable to transfer it back and the adult would thus be unable to fulfill the mitzvah.