I can't seem to beat dr.cid in king rathwalls tomb how do i beat him i go after the cystals no damage i go after him no damage what do i do?

There are two fights with Cid; the first is in Draklor Laboratories and the second is in the Pharos.

In the first fight, the Rooks needs to be destroyed before you can harm Cid. Cid uses guns, so you need to ensure your Gambits are set to accommodate heavy, quick damage to your party. Using Protect will be fruitless, so don't bother with it. Set the parties Gambits to Attack > Leader target. This way you'll take them out faster and ultimately save you a lot of casting time. After they're down, the fight's a breeze.

In the second fight, it's basically the same but without the Rooks. He's got a few stronger attacks but they're not really anything to worry about. After he receives around 50% damage of his overall HP, he'll cast a Paling that makes him immune to all damage. You'll not have to take out Famfrit before the Paling disperses, so make sure you're focusing solely on the Esper. Cast Shell to lessen the damage from his attacks and his powerful Waterja.