I wouldn't say they look so much rushed as I would say drawn as a whole, which can have a rushed look. I agree with Sparrowman about more than one tool, and it makes me want to ask a favor :3 My theory is that at the MINIMUM, a person should have two tools; a pencil and a pen. When I do legit pictures and not just doodles/sketches, I draw with a pencil and 5 pens (sizes .001, .01, .03, .05 and .08)
SO, what I would LOVE for you to do, is very lightly draw a SKETCH in pencil. Don't draw the whole person at first. First start with circles and lines to get the outline of the figure. Then sketch over that to draw an undetailed naked body. Then, in darker lines, sketch over that again to add clothes and details. THEN, haul out a pen, and draw over the dark lines and stuff, the "good lines" I call them. Wait 10 minuets or so, and erase the pencil so you're just left with the pen :3 And when drawing with the pen, don't be shy with the lines and just go nuts with them. Makes them light and loose. That sounds weird, but lol Imagine the letter S and the letter R. The letter S is a lot softer and looser looking than the letter R, so think of the letter S when you draw with the pen hahahaha.
You'll see part of what I mean soon, I'm waiting for youtube to upload some videos for me XD I made a couple pages of picture tutorials for you, and the rest are videos XD
And now that the suggestions are out of the way, lemme just say LOOK AT YOU!!!!!
!!!! I'm SO proud of yooouuu, you said you wanted to draw manga, and you're working so hard on it!!! You've improved SO MUCH from when you first started! You've improved SO much on spacing and style, it's obvious that you're getting a better grip on proportion, this just makes me so happy to see! SO HAPPY n_n you're doing a GREAT job, keep it up, you've improved SO much and all you can do is continue to improve!