I'm still working on my buffer so my comic is not up (I'm hoping for a September release date), but... Here's my cover:
It actually tells everything you ever need to know about the story, but it won't be obvious until the end 
Graphic design and composition has never been my strong suit so I find covers to be kinda challenging. Because you have to think of it with the text as part of the image and I am sooooooo bad at that. The habit I picked up recently that has been a bacon-saver is making sure to zoom out to like 8% and see if the cover still makes sense. Because that's roughly what your readers will see while they're glancing over hundreds of covers.