Most deworming solutions have instructions written on them; I'd take the snake to a vet first though, to verify it was just worms and nothing more complicated. There's no need to periodically worm the snake, I don't think, as it's not exposed (hopefully) to as many things as the common household pet. Too many meds can knock it for a loop, especially if it's not sick. I'd still ask the vet though, none of my snakes (nor the snakes I've had the chance to work with) have had worms.