Sephiroth...my long hated and respected rival, even in KH.
For KH1, the meteors might be some trouble avoiding: since they move closer and close towards Sepiroth, find a pattern in the movement that allows you to espace without much damage and not get caught up in his blast by keeping to the outer edge. Don't bother with Blitz or Combo Pluses: You'll only get to hit him 3-4 times before teleportation or before he starts attacking. Guard can be much more effective than Dodge Roll here, but keep both on.
Don't bother with magic attacks and refrain from MP-draining specials unless really needed: keep MP mainly for Curaga and Curaga only. Try to hit him before he starts Sin Harvest: having a keen eye and High Jump + Superglide equipped help. If you can't attack before than, keep a few seconds between when it hits and when you throw an Elixir up, since they take a while.
MP Rage/Haste helps to maintain your MP for Curagas needed. Second Chance might be a nice addition, too, but that's completely optional. Jackpot, Treasure Magnet, and Lucky Strike, as you'll have known, are completely useless here: though, if you're desperate enough, Ars Arcanum or Sonic Blade can help if you time reactions nicely. Just no strike Raid/Ragnorak. Strike Raid keeps you in place and firing at the same spot, which is worthless considering his teleportation and just makes you a target: Ragnorak's beams are completely dissolved by Sephiroth.
That's all I remember right now: another fight with him might refresh my memory, but I haven't gotten that far on my new data.