Even 12 hours of refrigeration will dehydrate rice,leaving it tough, dry, and sticky. There are a few rapid/fast methods of reviving it,so it tastes nearly as fluffy and light as the day it was made. No matter what your method of preparation, oil and a little liquid are the keys to helping rice retain its moisture and clump-free texture.
Reheat it in the microwave: For every cup of rice, or add a few tablespoons of broth or water. Cover the bowl of rice with plastic wrap or another bowl to create a steaming effect as it reheats.
Stir-fry it: In a large wok or sauté pan,heat canola or peanut oil on high. create a fried rice, breaking up the lumps of rice with a wooden spoon so the oil coats the granules evenly.
Stove-top steam it: In a sauce pan, or add the rice with a few tablespoons of butter and a splash of broth or water. Cover the pan and steam the rice on a low flame. Stir occasionally until the rice is heated thoroughly.
Source: popsugar.com