Where is the early bird when you need him?
Sand Worm's main attack is Swallow, which removes a party member from the battle for several turns. This is followed by Regurgitate, which will delay the regurgitated character's next turn, but he/she will be usable again. Ending the battle after a character has been Swallowed and before they have been Regurgitated will result in 0 AP being awarded to that character, as if they were in Eject status. Earthquake is Sand Worm's other offensive attack that will hit all party members, but takes several turns to cast.
The Sand Worm drops some particularly useful armor with Auto Potion and/or HP +10% as well as several empty slots. The weapons that it drops are not as useful with Magic +5%, Strength +5%, Slowtouch, and/or Piercing.
If Auron's Overdrive is unavailable, inflicting Darkness status and using a barrage of physical and magical attacks works best. Poisoning it via Bio will cause the Sand Worm to lose several thousand HP every turn. Having Rikku use Shadow Gems (which can be stolen from them) will also cause a lot of damage.