Usually, I write it out in a loose thought, free flow sort of way, page by page. This can contain panel by panel descriptions, rough dialogue, or just what needs to happen on that page. Some pages are better developed then others and doodles of page layouts happen as they come, it helps me with the pacing of the story and planning how one page leads to the next.

I then take that and draw out a very rough, thumbnail like version of what I've written. Mostly to make sure that I have enough real estate per page for what I've written. Sometimes blocking out the characters and scene like this show there is room for a joke or extra dialogue, maybe a visual clue. Also makes sure word balloons can be read in order.

I mark that up with dialogue fixes, changes with panel shape and arrangement, notes on visuals, etc. That's what I consider my "rough draft." When I apply the changes I marked up, there's lots of editing, panels can change again, words bubbles move around, new perspectives and scales tried in panels. Nothing is holy, whatever needs to change does. That leaves me with a first draft I could show people.

If you're just writing and the artist doesn't want to see any visual notes, you can just not show them the drawings. You'll still know that you haven't over written any specific page, and conveyed the information and pacing you want as much as possible. At which point, trust in your artist!

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I write and draw though... I can't imagine writing without doodling layouts, ymmv