Study Jessica Alba's films to get a feel for how she exudes a sexy yet strong confidence on the camera. Pay attention to her mannerisms and soft spoken manner but how it is juxtaposed with a strong intellectual center that provides validity and power to her physically alluring appearance.
Learn about Alba's life through searching the Internet and read various articles about her childhood and upbringing. Note her early struggles with religion and conservative values and her questioning of her family's beliefs and how that shaped her modern liberal views about women, religion, and sexual freedom.
Play up your own sexuality as Alba has done while tempering it with a healthy sense of humility and a sort of tongue and cheek recognition of your own beauty. Look at her most famous spreads in Sports Illustrated, FHM, and Maxim which have great interviews with the actress that provide a good balance to her highly sexually charged image.
Find something to advocate that you believe in. Jessica Alba works tirelessly to campaign for missing children and Habitat for Humanity because she strongly believes in helping the underdog. Do work with a charitable organization and get involved on the front lines to mimic Jessica Alba's dedication to humane causes.
Judge yourself and others by their character rather than on their physical appearance. Carefully play up your own sexuality while downplaying its importance; it's marketing genius that Alba has managed to pull off. Be yourself and always maintain an authentic and genuine presentation of all sides of yourself as a woman.