Cher Horowitz is a wealthy "Valley Girl" type who lives in a large mansion in Beverly Hills with her father, a successful $500-an-hour litigator. Cher's mother died in a freak accident during a routine liposuction procedure when Cher was just a baby. Cher is best friends with fellow rich girl Dionne Davenport who shares Cher's understanding of how it feels to be envied.
Cher loves to play the matchmaker and decides to bring two nerdy and low-grading teachers together. Although this is ostensibly so that she can soften them up to issue her with a higher grade, seeing their obvious happiness now that they have found love through her meddling Cher realizes that she enjoys doing good things and bringing happiness to others. With this in mind she decides to give back to the community by adopting a tragically un-hip new girl at school. Tai Fraser receives a makeover from Cher and Dionne which also has the result of making over her social life as well. They also attempt to teach her how to be popular and explain the mysteries if popularity. Tai is enamored of amiable slacker Travis Birkenstck, a skateboarder, but Cher decides to steer her away from him and towards popular snob Elton Tiscia instead.
Her second attempt at matchmaking is nowhere near as successful as her first. Her plan backfires completely when Elton rejects Tai and tries to seduce Cher instead. Although she has historically viewed dating during high school as a futile time-wasting exercise, Chet finds herself attracted to a new student called Christian Stovitz. In order to get his attention Cher sends herself flowers and live notes in an effort to spark a competitive spirit within him and inspire him to fight for her interest. Eventually Dionne's boyfriend Murray explains to Cher that Christian is immune to her advances as he is gay. Christian and Cher remain good friends primarily because she admires his taste in art and fashion.
Not only does Cher's attempt at matchmaking herself fall flat but Cher's project begins to work too well, and Tai's popularity soon surpasses her own, a hitherto unheard of circumstance. Events reach crisis point for Cher when she fails her driving text and cannot "renegotiate" the result. She returns home with the wind taken out of her sails to find Tai waiting for her; she confides that she has become attracted to Cher's step brother, Josh, and wants to enlist Cher's help in winning him. Cher tells Tai that Josh is wrong for her which prompts a quarrel. Feeling lost and "totally clueless" Cher begins to reflect on her priorities and her consistent failure when it comes to understanding the important people in her life.
After a great deal of soul searching, Cher realizes that her reaction to Tai's interest in Josh was so vehement precisely because she is interested in him herself. She makes rather awkward but genuinely heartfelt attempts to live a more meaningful life, captaining the school's Pismo Beach disaster relief effort. Eventually Cher and Josh admit their feelings for each other, confessions that lead to a long, tender kiss.
In a happy ending, Mr Hall and Miss Geist Wed; Cher's friendships with Dionne and Tai are strengthened; Tai and her skateboarder Travis are in love and Cher wins a two hundred dollar bet when she catches the bouquet at the Hall-Geist wedding. As the film closes she embraces Josh, and they share a much-anticipated kiss.