I would recommend reading books about writing comics before you actually attempt anything. I found a great book at my local library that interviewed artists and writers from mainstream comic producers. It was very interesting and showed a lot of the steps of producing a comic. There was a lot of information on the collaborative processes which had no relevance to me, but it might be for you.
Writing a comic is much like directing a movie. You determine "camera angles", script, pacing, etc. Some things have effects on the others, so I have found myself designing panel layouts that aid the story, or changing the story a bit to flow better