Hi! Welcome to Tapastic! I'm somewhat new myself, only having started last month.
Anyway, on to the review!
I like your concept. I think a lot can be done with that idea. I also like the gray-scale values, they look nice.
As for stuff to improve on, I have a bit of a list:
-Your buildings and other things look flat in 3D space or don't match the perspective at all. Be very careful with perspective. I know it's not easy--it's kind of hard for me too. Always plan your perspective, especially for an exposition shot.
-Your grammar could be better. Please have someone read over your stuff and double-check for you. It'll look less sloppy that way and your dialogue will be easier to understand. If English is not your first language, then it might be better for you to start out in your native language and translate it later.
-DON'T USE COMIC SANS! I know the font has the name "comic" in it, but that doesn't mean it should be used for comics or anything at all, really. It doesn't look good. It just makes everything feel cheap when you use it. If you want a new font, you can find some free ones here: Blambot.com
-Your human anatomy is okay in some places, but there are other places it starts to look goofy. I notice you're having difficulty with arms, hands, occasionally elongated torsos, and faces in profile. Try working from reference until you get those elements down.
-Try to keep your lines and shading inside the panels. It looks sloppy if you don't do that.
I hope this was helpful, fellow newbie. I'm trying to get better at my stuff, too.