Each issue's synopsis should not take up more space than a single page. Your best bet is to sent a couple of ideas to choose from, minimum three. If you give me some choices, there might be something that I like enough to ask for more or for clarification, etc. More times than not, I'll leave it. Do NOT send me long scripts or plots.
Every artist can do pretty pin-ups.
They really don't show me what you can do in the sense of story-telling. Try to include a variety. If you only send spandex super-heroes, I can't tell how you'd draw aliens. If you only send me aliens then I can't tell how you'd draw spandex. The key is some variety and panel to panel continuity.