Contact local modeling or talent agencies in the phone book. Ask when they'll have open calls or castings and find out what to bring to these calls. Check the newspaper classifieds for open modeling calls. Keep your antenna out for the ones that aren't legitimate. Also, watch out for agents who require you to use their in-house photographer, agents that ask for money up front, and a posted license inside the agency.
Most state governments require an agency to be licensed.
Finally, don't get discouraged. Rejection is a big part of the business. I bought a bright red sweater, but I have no idea what eyeshadow to wear with this. Choose matte shades of taupe, chocolate, cream, and pearly shades of eyeshadows. Concentrate on letting your skin glow in all its beautiful paleness, adding just a touch of peachy-bronze blush on the apples of your cheeks.