The minimum requirements for a kosher etrog that apply to all seven days of Sukkot are as follows: (i) it must be at least the size of an egg (there is no maximum size limit), (ii) it may not be round like a ball, (iii) it must be halachically edible as food and not subject to any shemittah, terumah or orlah eating restrictions, (iv) it must be free from certain types of blemishes that reduce its size (v) and it may not be the product of grafting with a lemon tree (murkav).
A feature that adds to the beauty of the etrog but is not essential is the pitam, which ideally should be in a straight line with the stem and have bumps and ridges. If the pitam has broken off, it is preferable to use another etrog, though many authorities hold that the broken etrog may be used on the first day of Sukkot as long as part of the pitam remains intact. If the pitam broke off entirely, the etrog may not be used on the first day of Sukkot unless it is the only etrog in town. It may, however, be used on the last six days of Sukkot. Of course, an etrog that never had a pitam is kosher.
The lulav must measure 12.4 inches along its backbone, and the te’yomet, the central leaf, must be double-leafed, closed, intact and straight. The hadas must have small triple leaves over a majority of the branch, should be between 9.3 inches and 11.4 inches long and the tip must be intact.
The aravot must have red stems, their leaves must be narrow and lip shaped, and they must be smooth-edged.
Other requirements, common to all the arba minim, are as follows: (i) On the first day of Sukkot, the arba minim must belong to the person using them and not be stolen or borrowed, since this would defeat the ulekachtem lachem requirement, (ii) on the first day of Sukkot the arba minim may not be dried out and withered since this defeats the hadar requirement which, according to some opinions, applies only on the first day, and (iii) they may not be subject at any time during Sukkot to condemnation for having been used in connection with idolatry.
In order to fulfill the mitzvah with a borrowed lulav on the first day, the owner should stipulate that he is giving the lulav to the user as a gift to be returned after use. According to some authorities, such a condition may be implied even if not expressed. Out of the same concern, the arba minim should be fully paid up before Yom Tov.
When the arba minim are picked up for the first time each Sukkot day, the blessing Al Netilat Lulav is recited all seven days and Shehecheyanu blessing is added on the first day. These blessings are recited with the etrog in the left hand, facing head down.
When the blessing is completed, the etrog is then turned the right way up. The reason for this is to allow for the blessing to be recited before the mitzvah is performed, in accordance with the rule of over leassiyatam. On Shabbat, no arba minim are taken because of the rabbis’ concern that this might lead to carrying the arba minim in the streets.
The arba minim are compared to the human being in prayer. The lulav symbolizes the backbone, the etrog, the heart, the hadas the eyes, and the arava the lips moving in the service of God.