In order to fulfil the Misva of Maror, one must consume a Kezayit (olive's bulk) which is 30 grams. This can be measured before Yom Tob. One must insure that the Romaine Lettuce used for Maror is properly checked for bugs. Some eat only the stalks because they are easier to check.
Before eating the Maror, the Beracha "Al Achilat Maror" is recited. The Ner Lesion discusses whether the Beracha is made before or after dipping the Maror in the Haroset. He cites the Rambam and others who seem to hold that the Beracha is recited first. Maran and the Ben Ish Hai seem to hold that the Maror is first dipped. Since he does not reach a definitive conclusion, one should follow the standard practice of first dipping in Haroset, shake a little off and then recite the Beracha. Of course, there is no leaning when eating the Maror.
The stage after the Maror is Korech, which is commonly called a sandwich, in which a Kezayit of Maror is placed between two pieces of Masa, which together amount to a Kezayit. Rabbi Mazuz (contemporary, Israel), in his new Hagaddah, states that the custom of Sepharadim is not to make a regular sandwich but to wrap the Maror around the outside of the Masa. He brings proofs from the Rishonim (early authorities), including Rabbenu Hannanel, Sefer Hahinuch and the Ben Ish Hai. In truth, the word "Korech" literally means to wrap, which also support that custom. Rabbi Moshe Shternbach in his Moadim U'zmanim also discusses this custom, citing the explanation of the Maggid Mesharim that this practice corresponds to the sequence of the redemption-first there was bitter slavery and then the freedom symbolized by the Masa. Rabbi Mazuz explains the custom of the Ashkenazim to put the Maror on the inside, because they used horseradish stalks for Maror, which cannot be wrapped, whereas Sepharadim always used the Romaine Lettuce. Either way, the most important thing is to actually eat both the Maror and Masa together. Thus, one must consume a total of two Kezayits of Maror-one for Maror and one for Korech.
Maran writes regarding dipping the Maror in Haroset "V'yishkienu Kulo"-he should completely immerse it in Haroset. Hacham Bension understands this to mean that the entire leaf should be dipped, as opposed to the Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933) who writes that just the tip of the Maror is dipped and then excess Haroset is shaken off. Although the Ben Ish Hai omits the word "Kulo"-completely, which may indicate that he did not hold that way. Ideally, one should dip the entire Maror in the Haroset. All agree that the Korech Is not totally dipped, as Maran does not use the expression "Kulo" regarding it.
It is best to partake of the Maror and Haroset from the Ke'arah (Seder Plate), although it is not always feasible that the Ke'arah contain enough for all the participants and more may be brought separately.
SUMMARY
The standard custom is to first dip the Maror completely submerged in the Haroset and then recite the Beracha. The Sepharadic practice is to wrap the Maror around the Masa, and not vice versa.
