The school is good for nudging Serena the right way, but IIRC, the trigger is the exhibitionist quest in Lovers' Park: Serena has to show the man enough clothes and skin to get him to suggest an update to her wardrobe. Serena should then be ready to buy sexy clothes (buy all of them now or eventually!). Reduce Shame I may be required also (from Eve). I'm not sure if the quest needs Serena to learn the Panties Off skill, i.e. be able to go commando. That is part of the Science Club's questline.
Someone asked this before, but I didn't see the answer.... Honey Select?
This sounds like you could be in the same position as the first question. The line you're seeing may refer to the sexy clothes sold by the shop next to the train station in town. Buy all of them. Serena should then wonder if Angie knows where to shop. If you are actually past this point and have the Black Suit, wear that to the park. Try with and without sexy underwear if at first you don't succeed. The short skirt allows Serena certain... freedoms. Further details are probably explained already in the thread.
