theres no real precedent for comic scripting, so its probably best you have a long talk with your artist about what each of you needs for your project to work. some artists do a lot better being left to it with the plot and dialogue, some want a great deal of clarity, down to panel layouts and shot descriptions and many are inbetween.
one thing to note, however: its best to have a description of a setting at the beginning of a scene that mentions any props or pieces of scenery that the characters interact with - otherwise, that coatrack might have to pop up out of thin air.