- One must ensure to chew the Maror, and to not just swallow it without tasting it; otherwise, one doesn't fulfill his obligation. .
- Even though Chazal enumerated five types of vegetables to satisfy the obligation of Maror, because we can't identify them one should use either Romaine lettuce or horseradish. Some say that horseradish is absolutely not maror.
- One shouldn't eat the Romaine lettuce together with horseradish.
How much Maror?
- The Maror should be dipped into the Charoset. One should wipe off the charoset and not dip it for too long otherwise it’ll remove the taste of the Maror.  Some only dip it partially. 
- Pesachim 115b
- Mishna (Pesachim 39a), Shulchan Aruch 473:5, Piskei Teshuvot 473:15. See also Definition of Maror by Rav Zvi Sobolofsky. Chazon Ish OC 124 writes that maror has to be left in the ground so that it is actually bitter.
- Rav Schachter (Inyonei Pesach 4 5778 min 10) quotes Rav Aharon Kotler who ate iceberg lettuce and Rav Soloveitchik who held it was specifically Romaine lettuce since that is what chazal had in Israel at that time. He explained that horseradish isn't considered maror. Rav Shlomo Amar (Motzei Shabbat Tzav 5778 min 2) also agrees that horseradish isn't maror at all.
- Rav Schachter (Inyonei Pesach 4 5778 min 11) explained that one shouldn't eat the Romaine lettuce together with horseradish since the horseradish isn't a mitzvah its taste nullifies the taste of the maror and one doesn't fulfill one's obligation.
- S”A 475:1. see also Amount of Maror by Rav Zvi Sobolofsky
- S”A 475:1
- Mishna Brurah 475:13
- S”A 475:1
- Mishna Brurah 475:14. Magen Avraham (475:6) writes that if one did indeed lean while eating maror one nonetheless fulfills his obligation. Rabbi Shmuel Loew in Machatzit Ha-Shekel finds support for this from the fact that Hillel must have leaned while eating maror since he ate it together with the matzah. However, Mishna Brurah (475:14) writes that if one so desires one may lean while eating the maror. Rabbi Hezekiah Silva in Pri Chadash (475:1) defends this approach by arguing that leaning is not a contradiction to slavery, for after all even the matzah and the first two cups of wine serve as partial symbols of slavery and are nevertheless leaned for.