Anyone have any suggestions or an online tutorial for sign language?

We have several deaf athletes at our gym and I also have a few deaf clients at my practice. I know enough to be dangerous but not enough to feel comfortable. I could be telling them "good job" or "your mayonnaise smells perky".

Most of our clients/athletes do a great job of reading lips but I've got some where the communication barrier can be frustrating for all of us. I can't teach them to hear so figured I'd learn to sign.

Any help is appreciated.