They don't care how much you know until they know how much you... Scratch that. First thing's first, they have to know who the heck you are. Some regular classroom teachers use their Interactive White Boards so exclusively that there's nowhere for a substitute to display his/her name. Make a (cute!) sign to take with you to every job. Works great if there's a document camera rigged up, but can also be taped to any vertical surface or pinned to a bulletin board.
Then you can get busy making sure they know you care.