When it comes to actual art technique, and your ability to draw, i'm afraid that's all on you. Nobody can snap their fingers and make you a better artist. ;) You've just got to keep practicing. My suggestion would be to just play around with different poses with each of your characters. Do a page with just expressions, etc. The more familiar you are with every nook and cranny of your characters, the easier it will be for you to draw them in a manga setting.
If you have the drawings you've done so far scanned and online post a link here and i can give you a few suggestions.
my artwork is here: [url]http://kilaria.deviantart.com[/url] and just like FireKnifeDancer said. Please do not steal my artwork, or my characters. They are mine and nobody elses.
Kilaria