When choosing songs, stick to material that falls into the kind of 'core' blues repertoire your fellow jammers will be most comfortable with. A jam set is not the place to break in new, obscure or unusual numbers. Likewise, don't expect anyone to be able to read sheet music or even charts.
Vocalists - as set-leader, it's your responsibility to call the songs clearly so that everyone else onstage knows what kind of number to expect. If it's a well-known blues standard, by all means give the title, but don't assume that everyone will know how it goes. Describe it. "medium shuffle in G, quick four, watch me for the stops" - that's the kind of information your fellow musicians need.