You’ll find Rikku on the shore ahead…talk to her to awaken her from her sleep. Afterwards continue on the path to Guadosalam, but in battle you’ll get a chance to practice with Rikku’s abilities. You’ll eventually reach Guadosalam, and by then you’ll learn how to customize your weapons with the help of a quick tutorial.
When you’re in Seymour Maester’s dining room, talk with your party members and after a long scenario you’ll get the shocking news. Afterwards head to the room at the top left part of Guadosalam, and on the floor is the Al Bhed Primer Vol.XIII. Now continue on to the top right(you’ll have to go through another ramp) to the Farplane. Pick up the Lightning Marbles just behind the bottom left braching area of the room, it’s a bit obscure.
You’ll have to leave to the Farplane without Auron and Rikku. Head over to Wakka to initiate the events, then talk with Yuna. Now afterwards head to the party in front of Seymour’s place. Talk with Lulu for a while and then talk with Rikku, who’s on the other side of Guadosalam. When Kimahri comes out of the shop he’ll tell you to buy some potions, do so and then go back and talk with Lulu. Then go to the entrance to the Thunder Plains, Shelinda will tell you that Maester Seymour has left…so what about Yuna? Talk with the other party members and head out to the Thunder Plains.