Me doing Ruby Weapon solo with Cloud! I also don't use any cheap Knights of the Round Miming like a lot of other people do to cheaply kill him.
The strategy is basic, but effective. Basically you have to keep feeding Cloud Hero Drinks (they raise your stats by a lot for one fight) while you continue to counter-attack after he has hit you.
You have to worry about the Tentacles, they can do some serious damage. One can hit you for about 9000 damage and the other can take away about 500 magic points. Make sure to Quadcast Cure 3 on yourself when you take a lot of damage. Your counterattacks will probably do the most amount of damage in this fight.
Strangley, Omnislash does not do that much damage to him, and the normal attacks are much better.