What are some tips to get a lower,softer, more hypnotic voice?

I don't want it to sound quiet or sound stuck up or snobby at all. I just want my voice to be more lower in tone and more seductress/femme fatale like. I want it to sound more elegant and hypnotic. An example would be like Uma Thurman of Poision Ivy from Batman and Robin or a girl version of Edward Cullen from Twilight Or even Scarlett Johansson maybe?. I need to practice for my acting cles and it's just something i want to know how to do. Thank you very much and many points to best answerer! I would appreciate this very much =)