Maran (Siman 472) writes that one should begin the Seder immediately after Arbit, so that the children should not fall asleep. Therefore, the Seder table should be set in advance, on Ereb Pesah. Even if someone was sitting and learning Torah, he should stop and get up to begin the Seder.
Nevertheless, one may not recite the Kiddush before dark, as is sometimes done on Shabbat. Since the Kiddush is one of the four cups, it must be done at the time fit for the rest of the Seder. The earliest one may make Kiddush is approximately half an hour after sunset.
Maran continues that one should use his finest dishes for the Seder. Unfortunately, people tend to do the opposite and use their lesser dishes for Pesah.
One should prepare his seat to be comfortable for reclining, to show our freedom.
