Have you gone into the Forgotten City to get Odin and evolve it into Raiden?

Have you un-cursed the Cursed Shield?

Completed Cyan's sidequest and obtain all his sword skills?

Found Duncan's house with Sabin in your party?

Seen all of Shadow's dreams?

Met Gung-Ho and battle the Hidon in order to get Strago's most powerful Blue spell?

Reunited Gau with his Dad?

Checked the beach on the island Celes was at for a year?

As for advice for the final area, its another 3 party dungeon with several boss fights. If you have been slacking with some characters and playing favorites, I would level them up and teach them a few magic or gain them a couple more skills if you can.