You said you're doing a story-based comic? Well, I have had issues with panel-layouts in the past - and sometimes still do; that stuff is hard! - and one of the things that has helped me is to pick out a comic that I enjoy, and going over the panel layouts in it and analysing them. When does the artist use what type of panel, and why? There's a rhythm and a point to how you lay out a a page.
Small panels read faster, and should probably be used when you want lots of stuff to happen in a short space of "time" (time is kind of a weird concept with a comic-page, since we see it all as one unit, but read it sequentially - comics are weird), while bigger, wider panels read slower, and are best used for establishing shots, or something that needs a lot of space - maybe a silent, significant moment in the story. Slanting panels, or characters breaking the borders of panels, are very effective in action scenes, etc., etc
And always keep in mind your wordballoons/speech bubbles! Plan them out from the beginning, so that you know where they will be on the final page, how much space they'll take up and if they'll read in a clear and easily understood order.
I always start off by doing thumbnails on paper - and in my case, that means literal thumbnails; none of my initial layouts are larger than 5 cm tall. It's just there to let me get an idea of what the layout will be like, and how much can fit into each page. Drawing them small and with a minimum of detail also means it's fast and easy to change them, if something doesn't look right.