The Shulchan Aruch writes that one’s table should be set from before nightfall so as to begin immediately [not this year! – since that would be hachanah on Shabbos for after Shabbos], and the Maharam Chagiz cites a tradition to set the table for the Seder three days ahead of time (in commemoration of the korban pesach, which was set aside and checked for three days prior to its sacrifice – including the day of the sacrifice, four days altogether). The Shulchan Aruch also writes that one should put his best and most ornate vessels on the table for the Seder. And, although the Shulchan Aruch would seem to indicate that it is the vessels needed for the Seder that should be the best and most ornate, the Maharil states that one who has nice vessels received from a non-Jew as collateral on loan should place them on the table – from which it may be deduced that even vessels that are not necessary for the meal should be placed on it if they are particularly nice.
R’ Hillel of Kalamai would adorn the Seder table with all the manuscripts he had written, saying that King David has taught us that Torah is more precious than thousands of gold and silver coins, and that, therefore, in putting his seforim on the table, he performed the act of adorning the Seder table in an even more effective way!
(Minhag Yisroel Torah 472:2)