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The most common these days is a "tactile" approach where one person uses sign language and the deaf-blind person holds their hands to "listen". There's research going on to make American Sign Language more streamlined to support this sort of interaction, but while that's doing on, in the US at least, it's common to have people just sign ASL. https://www.youtube.com/watch?v=9GrK3P15TYU

Blindness is a spectrum though so it's possible that some deaf-blind people will have some sort of ability to see (usually takes the form of tunnel vision). In that case, they can still communicate similar to deaf individuals but it's usually modified so that the hands remain much much closer to the face (stay within view of what they can see).