I find it a terrible calamity for the mankind that people want to draw manga. I always find it a bit weird to copy someone else's style and not look for your own. Especially when there are also people who think manga as "a way of making ugly drawings seem reasonable" (not that this would be happening here, referring to some things at DA).
But I guess that can't be helped, so go on. I hope drawing "anime" will teach you things you can use later on to create your own distinct style. Sorry for the rant-like post; draw as much as possible and whatever you want, but in the end, try to search for your own way of drawing!
Evil: I fear that this may come out as ranty-sounding or useless or evil or something like that, but indeed, in drawing the most important thing is just to draw constantly and as often as possible, just to make yourself better at it. People that have got a good grasp of drawing/painting may draw/paint very cool characters/scenes even without knowing anatomy or perspective or such. The examples you've shown here don't really show how well you've got hang on drawing (they look nice, but they're quite simplistic) so it isn't easy to say anything about what to do next or how the pictures actually look. I think it might be best to just draw a lot in different styles instead of trying to start using a special style, it'd be a very good way to learn eye for design.
Didriking: You seem to have somewhat of hold of the face, apart from the eyes - the sketches look fine. I suggest you start next learning some more body anatomy; when drawing full characters, it comes in really handy. Also you might enjoy trying a bit more natural and smaller eyes? They're currently quite big compared to the other face.
EDIT: Oh, and looks like the definition of "what's anime & manga" was argued and then described rather well. Cheers!