I'd recommend getting the Signing Naturally Series (Dawn Sign Press)... you can often borrow these from your local library, a College/University library, or Deaf centre library. If not , they're still not terribly expensive, and "the standard" used in many ASL classes. Another "standard" book is the ABC book ( A Basic Course in American Sign Language) - also available via dawn sign press.
Truthfully though ... see if you can enroll in some ASL classes in your area. If you've already taken the classes and got rusty, maybe take them again for audit? Many areas also have Deaf socials quite frequently ... or Deaf Coffee nights - and you'll likely learn more in one evening there, than a week starting at a computer screen.
