Contact a school for the deaf, if you are lucky enough to have one in your area. A school will have the best resources for learning American Sign Language, with classes geared toward the family and friends of deaf people.
Ask a deaf person to teach you sign language. The person will likely be impressed with your willingness to learn a language that will better able you to communicate with him.
Visit your library or bookstore. There are many books, CDs and DVDs you can rent that will instruct you in sign language.
Call any community colleges in your area. They may have continuing education classes that you can take to learn the language. Some schools may even offer you college credits.
Look in your telephone book for any associations for deaf people. They will be able to direct you to places where you can learn American Sign Language.
Visit a website that teaches sign language. This may be a more effective way to learn the language if you do not have time to attend a formal class.