One may use for Marror either the leaves or the stalk of the romaine lettuce. Since stalks are usually not contaminated with insects to the same extent as the leaves, some people prefer using the stalks (though the stalks must also be checked). If one chooses to eat the leaves, he must ensure that they are moist at the time when he eats them. It is advisable to wrap the leaves in a damp towel or cloth to keep them moist for the Seder. If one prefers to soak the leaves in water, he must ensure not to leave them in water for twenty-four consecutive hours. Vegetables soaked in water for this period have the Halachic status of Kavush ("pickled"), and one does not fulfill the obligation of Marror with pickled vegetables. One should therefore either soak the lettuce for less than twenty-four hours, or wrap them in a moist cloth, as mentioned. [Chazon Ovadia, page 95.]
One must endeavor to eat the Marror before Chatzot (midnight as defined by Halacha); if one does not eat Marror until after midnight, then he does not recite the Beracha of "Al Achilat Marror." [Chazon Ovadia, page 100.]
After eating the Marror, one proceeds to "Korech," which requires eating a Ke'zayit of Matza together with a Ke'zayit of Marror. One should use for Korech the bottom of the three Matzot that he had before him until this point in the Seder. Of course, this single Matza will not suffice for distributing a Ke'zayit of Matza to every participant in the Seder, and therefore one should take as well Matza from the box on the table. One dips the Matza-Marror combination in Charoset, recites the "Zecher Le'mikdash Ke'Hillel" as printed in the Haggada, and then eats the Matza and Marror as he leans on his left side. If one forgot to lean while he ate the Korech, he should preferably repeat Korech, unless he finds this difficult, in which case he may, according to Chacham Ovadia Yosef, be lenient. Similarly, if one forgot to dip the Korech in Charoset before eating it, he should preferably repeat Korech, unless he finds this difficult, in which case he may be lenient. Even then, however, one should eat at least a small quantity of Matza and Marror with Charoset (Chazon Ovadia – Laws of Pesach, p. 101). Before eating the Korech one need not shake some Charoset off, as one must before eating Marror.
It is improper to add any other foods to the Korech; the Korech should consist of only Matza and Marror dipped in Charoset.
Upon completing the Korech, one proceeds to the festive "Shulchan Orech" meal. One should not engage in any speech unrelated to the Mitzvot of the Seder from the time he washes his hands for Matza until he completes Korech. Some people make a point not to speak at all until after eating the Afikoman at the end of the meal, other than in words of Torah and songs of praise to God. [Chazon Ovadia, page 109.]