Wear "Imperial Army uniform" (if you brush imperial army monsters in Baiwulin, you may lose them), and brush "Qingtianmeng Disciple" in Baiwulin "Qingtianmeng Base" for a certain amount (generally 15 or so). Zheng Zhongsheng, captain of the Blue Sky Dream Guard, and two members of the Red Flower Club will appear. Beat them and you can get two "Blue Sky Dream Badges".

2. After collecting the 100 Blue Sky Dream badge, you can go to Baiwulin Observatory, the observatory on the right (you can fly there), and ask NPC to put on the apprentice costume of Blue Sky Dream.