Rayquaza's best moves are Surf, Flamethrower, Thunder, Hyper Beam. These moves are great because if there is a fire/rock pokemon, use Surf, if there is a water/flying pokemon, you can use Thunder, if there is a bug/grass pokemon, you can use Flamethrower, and if there is a diffrent type of pokemon, blast it with Hyper Beam. Since Rayquaza starts at Lv. 70, the moves are already ultra powerful.