1. One should not remain in the Sukah if it rains.
2. The Gemara discusses leaving the Sukah in the middle of a meal due to rainfall.
3. The Gemara discusses leaving the Sukah in the middle of the night due to rainfall.
4. The Mishnah (28b) says that when it rains on Sukos it is like a servant who wants to serve but ends with the "spilling of a jug."
5. A stolen or dry Lulav is invalid.
A BIT MORE
1. One who is very sensitive, such that he would become distressed if wind would cause some pieces of Sechach to fall into his food, is exempt from the Mitzvah of Sukah.
2. If the rain stops after he already resumed his meal in the house, he is not required to return to the Sukah to finish his meal.
3. If one went back into the house to sleep, he is not required to return to the Sukah in the middle of the night even if the rain stops.
4. The Gemara explains that this means that it is like a servant who wants to serve his master by diluting his wine with a jug of water. The master is upset at the servant and therefore spills the water on the face of the servant as if to say, "I do not want your service."
5. A Lulav of an Asheirah tree (idolatry) or of an Ir ha'Nidachas (a city destroyed because most of its inhabitants committed idolatry) is invalid.